Science Writing – Who to write like…

In their 1953 “Molecular Structure Of Nucleic Acids” Watson and Crick open with the decidedly unscientific “We wish to suggest…” and in only a short page or so, take us through their thoughts on what shape DNA takes in the natural world. With a tone, that is though decidedly academic, conversational in the way it winds from chemistry to other laboratories take on what structure DNA might take.

The paper is notable for what is not present as well. After a careful description or at least inventory of the facts supporting their structure, they proceed to open up a new avenue of discusion; suggesting how the model might relate to the observed biology. In one of the final paragraphs they lead with “It has not escaped our notice…”. They hint that the structure they have described, suggests that there is a very simple solution to another vexing problem remained unsolved in 1953. How does DNA copy itself, and how does it do so quickly?

Here Watson and Crick speculate that they have solved an important piece of this puzzle, and interestingly do so without directly stating what their speculation is! As is to pass off the impoliteness they assure us that these speculations and more data will follow.

They write as if they are dashing out the door, when in fact they seem to have carefully crafted their thoughts so the reader can follow the unfolding story as if discovering the structure themselves.

If you are in Tox 1401, I want you to carefully read the paper and using a tone and style similar to Watson and Crick describe the three dimensional structure of DNA. The exercise here is not only think about science, but to focus on how it is communicated. After your description, add a short speculation on what other structures DNA might take. Your structure can be made up, but I want to to root your structure in some facts, much like Watson and Crick do. You may have to rewrite this piece a few times before committing it to the blog. Take the time to look over what others have written, and comment on well crafted descriptive pieces.

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101 thoughts on “Science Writing – Who to write like…

  1. The DNA is a double stranded helix with the two strands connected by hydrogen bonds. Each spiral strand is composed of a sugar phosphate backbone that is attached to bases. The bases are on the inside of the helix and phosphates on the outside. The backbone is constructed from alternating deoxyribose sugar and phosphate molecules, which are highly polar. Therefore, the backbone is polar, and it is hydrophillic. The interior portion of the DNA molecule is composed of a series of four nitrogenous bases: adenine, guanine, thymine, and cytosine. These bases are nonpolar and therefore hyrdophobic. These bases are complementary to each other and there is hydrogen bonding between these paired bases, where adenine pairs with thymine and guanine pairs with cytosine.

    The DNA double helix is right handed, where the nucleotides are linked to each other by their phosphate groups, which bind the 3′ end of one sugar to the 5′ end of the next sugar. This makes the DNA antiparallel, which means the 5′ end of one strand is paired with the 3′ end of its complementary strand and vice versa. Therefore, the two strands of DNA have opposite chemical polarity so their sugar phosphate backbone runs in opposite directions. The direction in nucleic acids is specified by the carbons of the ribose ring in the sugar phosphate backbone of DNA. The 5′ specifies the fifth carbon in the ribose ring, and 3′ specifies the third carbon in the ring. Therefore, the direction of DNA molecules is specified by these carbons.

    A structure for DNA was proposed by Pauling and Corey before Watson and Crick. They proposed a triple helix but their model failed to predict the structure of DNA. In their triple helix model, the phosphates formed the helical core with the bases pointing outward. In my opinion, this structure is unacceptable because it would be impossible to have such structure in normal cellular conditions. Each phosphate group is negatively charged and so many negative charges forced together would repeal each other. In reality, this would drive the structure apart. Therefore, I like Watson and Crick’s DNA model better. I like the fact that in their model bases forms the helical core with the phosphate pointing outward.

    Although Watson and Crick’s DNA model is great, I would like to propose a structure of DNA similar to theirs with one exception. In my structure everything stays the same but a third DNA strand is added to the double helix. The scientific possibility of a triple helix has been known for a quite some time. It has not escaped my mind that no known scientists have found a third DNA strand. But I think a third DNA strand is perhaps not yet visible with our scientific instruments. I think if we look at most pictures of the double helix, we can see that there is clearly room for additional parallel strands. There is also scientific proof that additional strands can fit into the DNA structure. I think scientific understandings are always changing as we gain new knowledge, so why can’t we have a triple helix.

    • PLEASE READ AND COMMENT ON REVISED VERSION OF MY BLOG BELOW BECAUSE IN THE ABOVE VERSION OF MY BLOG I PROPOSED A STRUCTURE OF DNA AND GAVE REASONING BUT I DID NOT DESCRIBE IT SO READ AND COMMENT ON THE REVISED VERSION BELOW. THANK YOU!!!

      • REVISED VERSION

        The DNA is a double stranded helix with the two strands connected by hydrogen bonds. Each spiral strand is composed of a sugar phosphate backbone that is attached to bases. The bases are on the inside of the helix and phosphates on the outside. The backbone is constructed from alternating deoxyribose sugar and phosphate molecules, which are highly polar. Therefore, the backbone is polar, and it is hydrophillic. The interior portion of the DNA molecule is composed of a series of four nitrogenous bases: adenine, guanine, thymine, and cytosine. These bases are nonpolar and therefore hyrdophobic. These bases are complementary to each other and there is hydrogen bonding between these paired bases, where adenine pairs with thymine and guanine pairs with cytosine.

        The DNA double helix is right handed, where the nucleotides are linked to each other by their phosphate groups, which bind the 3′ end of one sugar to the 5′ end of the next sugar. This makes the DNA antiparallel, which means the 5′ end of one strand is paired with the 3′ end of its complementary strand and vice versa. Therefore, the two strands of DNA have opposite chemical polarity so their sugar phosphate backbone runs in opposite directions. The direction in nucleic acids is specified by the carbons of the ribose ring in the sugar phosphate backbone of DNA. The 5′ specifies the fifth carbon in the ribose ring, and 3′ specifies the third carbon in the ring. Therefore, the direction of DNA molecules is specified by these carbons.

        A structure for DNA was proposed by Pauling and Corey before Watson and Crick. They proposed a triple helix but their model failed to predict the structure of DNA. In their triple helix model, the phosphates formed the helical core with the bases pointing outward. In my opinion, this structure is unacceptable because it would be impossible to have such structure in normal cellular conditions. Each phosphate group is negatively charged and so many negative charges forced together would repeal each other. In reality, this would drive the structure apart. Therefore, I like Watson and Crick’s DNA model better. I like the fact that in their model bases forms the helical core with the phosphate pointing outward.

        Although Watson and Crick’s DNA model is great, I would like to propose a structure of DNA similar to theirs with few exceptions. In my structure, a third DNA strand is added to the double helix. The scientific possibility of a triple helix has been known for a quite some time. It has not escaped my mind that no known scientists have found a third DNA strand. But I think a third DNA strand is perhaps not yet visible with our scientific instruments. I think if we look at most pictures of the double helix, we can see that there is clearly room for additional parallel strands. There is also scientific proof that additional strands can fit into the DNA.

        In my DNA structure, the third strand binds specifically in the middle between the double strands of DNA where the complementary bases pairs. This DNA structure looks like a star fruit with three ridges. These three strands wraps around one another like the weaving of a rope. Each one of these strands combines to form a triple helix with bases in the middle. These bases are attached to a sugar phosphate backbone where the phosphate groups are on the outside. The interior portion of the DNA molecule is composed the four nitrogenous bases: adenine, guanine, thymine, and cytosine. These bases are complementary to each other and there is hydrogen bonding between these paired bases.

        The bases from three strands will combine to form base triplets. In such situation, a thymine from the third strand binds to an adenosine and thymine paring and form a thymine to adenosine to thymine base triples or a cytosine from the third strand binds to a guanine and cytosine paring and forms a cytosine to guanine to cytosine base triples. This triple helix is right handed, where the nucleotides are linked by their phosphate groups. The DNA is antiparallel with the triple helix, which means the 5′ end of one strand is paired with the 3′ end. Therefore, their sugar phosphate backbone runs in opposite directions. I think scientific understandings are always changing as we gain new knowledge, so why can’t we have a triple helix.

      • Ummea Urmi:
        Your piece was straight to the point and descriptive especially when you described the DNA structure. Anyone who read this would have a clear understanding because of how well you structured your response. Remaining focused on the topic at hand and using the scientific language were great techniques that you used to make this similar to Watson and Crick’s description of the DNA structure.

    • I think this was very well written, especially the explanation of the structure of DNA. It was very specific and not confusing, so it was explained and depicted very well. I did read the revised version, and I think it did a better job depicting the style of writing of Watson and Crick. I also thought it was very interesting of the proposal of a third strand of DNA.

    • Comment on Adedayo Oduwole

      I thought your description of the DNA structure was very good. It was very interesting how you mentioned the mass spectrometry, 13CNMR, 1HNMR, and infrared techniques that we are now learning in organic chemistry. It was nice that you analyzed these data that you mentioned when you said that these strands of DNA seem to match the chemical composition of a phosphate and a sugar according to these tests. Also, I think the single structure of DNA that you mentioned which wrapped around a single axis is really good. Especially when you mentioned that theses strands are composed of alternating anion and cation bases. The magnetic field that you mentioned was a nice touch where electrical gradient between the two molecules holds the entire chain in place. I agree that the interaction of the electrons will create a magnetic field causing the bases to probably line up if their chemical composition allows this to be energetically favorable.

      Comment on John Hang Leung

      I thought of the same idea that you mentioned about the triple helix. I think you probably read it and I agree with the triple helix totally. The third strand of DNA might seem quite strange but it is not impossible because DNA has space to put the third strand. It was very interesting that you mentioned that this information could be used to track down the gene expression by knowing the structure of DNA. I think to know the true structure of DNA we needs more advance technologies to see the structure of the DNA better. I loved the fact that you mentioned that the triple helix structure of DNA plays an important role in gene expression and recombination. It was interesting that you mentioned genetics in your response. I also thought your description of the DNA was also very good. It was very informative and I thought it was nice that you mentioned the importance of DNA since it carries the specific genetic information in the chromosome which is known as gene.

  2. The structure of deoxyribonucleic acid (DNA) within the cells in organisms is essentially important in biological and genetic study. Its importance is because not only it is an essential constituent of the chromosome, but also it carries the specific genetic information in the chromosome which is known as gene. Although many evidences indicate that the results of the structure of DNA are ladder-like molecule and double- stranded helix forms; however, it does not escape the notice that the DNA structure would always form in the double- stranded helix structure.

    In deoxyribonucleic acid (DNA), two strands that are anti parallel each other connect together by hydrogen bonding between the base pairs to form the double- stranded helix structure. Each strand is formed by several nucleotides, consisting of phosphate, sugar, and base. Four different bases: adenine, guanine, thymine, and cytosine were found in the DNA. Additionally, adenine and guanine are known as purines while thymine and cytosine are known as pyrimidines. It was also found that these four bases pair specifically which adenine pairs with thymine, and thymine pairs with cytosine. These specific paring is strongly supported by the analytical results that show the amount of adenine is close to the amount of guanine, and the amount of thymine is close to cytosine.

    However, the unusual three-stranded structure known as triplex DNA structure, forms when a single-stranded region of DNA pairs with a paired duplex DNA helix through additional hydrogen bonding between the bases of all three strands. The formation occurs due to the Hoogsteen bonds, which form between bases in the incoming single-stranded DNA and the already paired bases in the duplex. The triplex DNA structure plays an important role in gene expression and recombination. It also acts as inhibitors of gene expression. Triplex structures have been studied in solution by NMR, but have hitherto resisted attempts at crystallization.

    Despite DNA often forms double- stranded helix structure, the other structures can arise such as triplex and quadruplex. These structural differences can influence the gene expression and mutations may occur. Therefore, this information could be used to track down the gene expression by knowing the structure of DNA to the related syndromes.

    • Comments:
      To Ummea Urmi: I found that your response is pretty clear in describing the DNA structure. In addition to this, I also agree with that there is triple helix structure exists in DNA. I have pretty much the same thought with you that “I think scientific understandings are always changing as we gain new knowledge, so why can’t we have a triple helix.”
      To Lauren DiRe: I like the description of your response which I also have the same belief that triple helix stranded DNA structure would occur rather than double helix. I also agree with you that “one day with better technology, such as stronger microscopes, this possible third helix can be viewed.”

      • Indeed, it turned out later that the triple helix does indeed exist in side of the cell and that it is required for life. It shows up as a “D-loop” in telomeres, the structures that keep our chromosomes from getting shorter and shorter. Turns out the more you know… the less you know.

    • I thought of the same idea that you mentioned about the triple helix. I think you probably read it and I agree with the triple helix totally. The third strand of DNA might seem quite strange but it is not impossible because DNA has space to put the third strand. It was very interesting that you mentioned that this information could be used to track down the gene expression by knowing the structure of DNA. I think to know the true structure of DNA we needs more advance technologies to see the structure of the DNA better. I loved the fact that you mentioned that the triple helix structure of DNA plays an important role in gene expression and recombination. It was interesting that you mentioned genetics in your response. I also thought your description of the DNA was also very good. It was very informative and I thought it was nice that you mentioned the importance of DNA since it carries the specific genetic information in the chromosome which is known as gene.

  3. The structure of DNA is very unique. It is made up of a double helix, in which two phosphate sugar chains, containing nitrogenous bases are held together by hydrogen bonds. These chains run anti parallel to each other, each containing a sequence of bases that matches up with its coordinating base on the opposite phosphate chain. Along these chains, a random sequence of nitrogenous bases can be found. The bases along the chains can only be one of four-adenine, thymine, guanine, or cytosine. Adenine can only pair with thymine and guanine can only pair with cytosine. Adenine and Guanine are purines, while Thymine and Cytosine are pyrimidines. Given this information, if only one chain is present, it is easy to determine its matching sequence. Aside from the fact that phosphate molecules are polar, it can be assumed that the phosphate sugar chain is hydrophilic, because they are the outer most part of the structure. Assuming that the phosphates chains are hydrophilic, the nitrogenous bases must be hydrophobic since they are the inner most part of the structure. The DNA molecules is right handed in which the phosphate chains run anti parallel to each other so that one chain is always running in the 3’ direction and the other is running in the 5’ direction. Although a very small molecule, DNA plays a very large role in making us ‘who we are’. DNA carries genes, which control both our physical and chemical makeup.

    Given this information about the DNA molecule, it is quite possible that there is a third helix. It is known that the structure of DNA is very open, making it possible for a third helix to fit in between the double helix. Perhaps this third helix is located in the middle of the outside double heli, that is known of now, and it is thinner than the outside two helixes, which is why it isn’t seen now. Like the double helix, this helix too, has base pairs along its insides.One day with better technology, such as stronger microscopes, this possible third helix can be viewed.

    Comments:
    To Ummea Urmi: I completely agree with your proposal of a possible triple helix and I find that it is a very interesting point. I can see how this could be possible since the DNA molecule has a lot of wide open space. I also agree that with the point that there very well maybe a third helix, and it just isn’t visible I really enjoyed your description and speculation. It was very well written and well researched.
    To John Hang Leung: I really like your connection between gene expression and related syndromes. I think that tracking gene expression is crucial to ‘fighting’ certain diseases and syndromes, and that if more information is found about genes, than better ways of treatment can be found.

    • I agree that there might be a 3rd strand on the outside. I was just wondering if there was a 3rd stand how would the base pairs work. Would all 3 of the base pairs just fuse together somewhere in the center? When I look at the double helix model, I can see that there probably be enough space to fit a 3 strand. Maybe a fourth?

      I also agree that the foundation of science is dependent on the technology we have. With limited resources, one can only get so far. If there was better technology, one might just see something someone else could not.

      • Technology is always an issue, and in truth, the limits of technology are often one of the reasons that scientists speculate. In those cases, we can perform theoretical experiments, hypothesizing on what we think might or might not happen. This pushes the limits of what we know and also suggests how a new technology might be used.

    • The way you explained the structure of DNA was also very well written. Like I wrote before on someone elses’, I also like the proposal of having a third strand. The writing of Watson and Crick was not very similar, however, I still liked how concise and clear you were when you described the structure of DNA.

    • The possibility of a third helix is more than just a possibility nowadays. It might even be found in other species that have evolved more rapidly and will eventually be in humans. The question is if it will be more stable than the structure that is currently found in humans or will it be more susceptible to mutations and errors, especially during duplication. Although the body has naturally made correction enzymes whose job it is to fix DNA errors during copying, added another strand means more chances of mistakes. And what about the idea of the leading and lagging strands. Which one will be copied first and how will the others follow? I think if those ideas are understand, even if evolution cannot fix genetic problems, possibly man can make the attempt.

    • You did an awesome job explaining the structure of DNA. I was able to understand clearly, and your phrasing seemed to flow; which I liked. I agree with your speculations about a third helix. I think that the DNA structure that Watson ann Crick propose, seems a bit too wide to only accomodate 2 strands. A third strand looks like it can fit in that open space.

  4. DNA is a thin, chainlike molecule found on every living cell on earth. It directs the formation, growth, and reproduction of cells and organisms. DNA is found in mainly within a cell’s nucleus, in structures called chromosomes. DNA consists of thousands of smaller chemical units (nucleotides). There are four DNA bases: Adenine, Guanine, Thymine, and Cytosine. A nucleotide has only three parts, a phosphate group, 2-Deoxyribose, and an organic base. The structure and orientation of a DNA strand showing the direction of synthesis from 5` to 3`.DNA does not normally exist as a single strand, it has a tendency to associate with another, complementary strand. The strands wind together through space in a helical fashion which is described as a double helix. The two sugar-phosphate backbones are on the outside of the double helix, and the bases project into the interior. The adjoining bases in each strand stack on top of one another in parallel planes. The orientation of the two strands is antiparallel (their 5` > 3` are opposite); they are held together by the cooperative energy of many hydrogen bonds in addition to hydrophobic interactions. The opposite strands are held in precise position by a regular base pairing between the two strands. A is paired with T by two hydrogen bonds; G is paired with C by three hydrogen bonds. To maintain the geometry of the double helix, a larger purine (A or G) must pair with a smaller pyramidine (C or T). In theory either purine could pair with either pyramidine, but in natural DNA A pairs with T and C pairs with G. The exact amount of each nucleotide and the order in which they’re arranged are unique for every kind of living thing and that’s what makes us so different. DNA without a doubt is probably one of the greatest wonders most important to the existence of life.
    As I wrote about DNA molecule, it can be possible that there is a third helix.I think the scientific instruments is not quite developed to see the third strand of DNA. But DNA technology is the most leading sciences going in to 21st century.One day with better technology, such as stronger microscopes, this possible third helix can be viewed and scientist will discover somenthing new in DNA and maybe it helps to cure or eliminate such diseases or deformities as AIDS or down syndrome.
    Comments:
    To Lauren DiRe:I agree with your idea about third strand of DNA and its quite possible because DNA has many open rooms where third strand can be.I also agree with the idea about technology that it is not well developed so scientist can’t see it yet.I like your responce its written very interesting and easy to read and understand the material.
    To Ummea Urmi:I really like your responce its well researched and written very interesting. I completely agree with your thoughts about triple helix and I think it very good idea. It can be possible but the scientific instruments are not well develop so it cant be seen yet.

  5. DNA is a thin, chainlike molecule found on every living cell on earth. It directs the formation, growth, and reproduction of cells and organisms. DNA is found in mainly within a cell’s nucleus, in structures called chromosomes. DNA consists of thousands of smaller chemical units (nucleotides). There are four DNA bases: Adenine, Guanine, Thymine, and Cytosine. A nucleotide has only three parts, a phosphate group, 2-Deoxyribose, and an organic base. The structure and orientation of a DNA strand showing the direction of synthesis from 5` to 3`.DNA does not normally exist as a single strand, it has a tendency to associate with another, complementary strand. The strands wind together through space in a helical fashion which is described as a double helix. The two sugar-phosphate backbones are on the outside of the double helix, and the bases project into the interior. The adjoining bases in each strand stack on top of one another in parallel planes. The orientation of the two strands is antiparallel (their 5` > 3` are opposite); they are held together by the cooperative energy of many hydrogen bonds in addition to hydrophobic interactions. The opposite strands are held in precise position by a regular base pairing between the two strands. A is paired with T by two hydrogen bonds; G is paired with C by three hydrogen bonds. To maintain the geometry of the double helix, a larger purine (A or G) must pair with a smaller pyramidine (C or T). In theory either purine could pair with either pyramidine, but in natural DNA A pairs with T and C pairs with G. The exact amount of each nucleotide and the order in which they’re arranged are unique for every kind of living thing and that’s what makes us so different. DNA without a doubt is probably one of the greatest wonders most important to the existence of life.
    As I wrote about DNA molecule, it can be possible that there is a third helix.I thinks the scientific instruments are not quite developed to see the third strand of DNA. But DNA technology is the most leading sciences going in to 21st century. One day with better technology, such as stronger microscopes, this possible third helix can be viewed and scientist will discover something new in DNA and maybe it helps to cure or eliminate such diseases or deformities as AIDS or Down syndrome.
    Comments:
    To Lauren Dire: I agree with your idea about third strand of DNA and it’s quite possible because DNA has many open rooms where third strand can be. I also agree with the idea about technology that it is not well developed so scientist can’t see it yet. I like your response it’s written very interesting and easy to read and understand the material.
    To Ummea Urmi: I really like your response its well researched and written very interesting. I completely agree with your thoughts about triple helix and I think it very good idea. It can be possible but the scientific instruments are not well developed so it can’t be seen yet.

  6. Several scientific research and evidence suggests that deoxyribonucleic acid (DNA) is a three-dimensional helical structure comprised of two chains. These chains run anti-parallel to one another and are made up of phosphate bases. When analyzed via, mass spectrometry, 13CNMR, 1HNMR, and infrared techniques, the strands of DNA seemed to match the chemical composition of a phosphate and a sugar. Thus, it can be inferred that both a sugar and phosphate make up the backbone of DNA. The sugar was further processed and contained identical functional groups and atomic mass as the deoxyribose sugar molecule. There are four nitrogen bases which make up DNA: adenine, thymine, guanine, and cytosine. Each base seems to have a certain binding preference for another base. Experimentally, adenine, thymine and cytosine, guanine were both found in equal amounts within a DNA sample. Thus the following conclusion can be made. Adenine has a binding specificity for thymine and guanine has a binding specificity for cytosine. It is unknown whether under certain conditions a base will undergo a physical or chemical conformation in order to combine with a different base. For example: In the absence of thymine, would adenine bind to guanine, cytosine, or even itself? What changes would ensue due to these changes? If these changes are made, could the DNA strand be transcribed into an mRNA and translated into a protein? The answers to these questions are unknown. However, this recent advancement in the study of DNA could help other scientist develop techniques to help answer these questions and expand scientific knowledge on DNA and other molecules.
    I also believe another structure of DNA exist as a single stranded chain wrapped around a single axis. The strand is probably composed of alternating anion (negatively charged) and cation (positively charged) bases. The electrical gradient between the two molecules holds the entire chain in place. The interaction of the electrons seems to create a magnetic field causing the bases to probably line up; if they’re chemical composition allows this to be energetically favorable. Another structure that could possibly describe the structure of DNA is a zig-zagged zipper. Each base it tightly zipped together with the other bases surrounding it. Each base is attached to 3 other bases and the middle axis serves as the single backbone supporting the addition of the four bases.
    @Lauren DiRe:
    It is difficult to write like someone else, but you did a good job writing like Watson and Crick did in the article. I couldn’t picture DNA having 3 backbone structures because I feel like there would be a point were all three would have to intersect and I feel the that molecules such as RNA polymerase would always be unable to code for a different length of DNA. This would probably minimize the variation of mRNA and proteins.
    @ John Hang Leung:
    It’s very hard to try and emulate another person writing. You didn’t really include as many speculations or assumptions, but you did describe a DNA strucutre that I dont think anyone else came up with. A quadruple-helix is very unique and complex. I feel like when all four backbones combine together they would probably force the RNA polymerase to stop transcibing the gene. I wonder, when you unwravel the quadruple helix would it be 4 several seperate backbones or like 4 slikys shoved together? Interesting structure.

    • This is a really nice response to the article, i enjoyed your style of writing and it was actually very informative. I liked how you thought of different structures for DNA like the single stranded example, which you said could be plausible if the electric gradient is aligned correctly. This seems rather interesting, i never thought the anions and cations could play a role in the shape of the DNA molecule, its quite the intriguing thought.

    • Great that you noted the observation grounding equivalent amounts of A:T and G:C. It seems odd to think about now, but there were plenty of models that allowed C:T or G:A and others. It was this “equivalency” that provided support for the Watson/Crick model.

  7. Several scientific research and evidence suggests that deoxyribonucleic acid (DNA) is a three-dimensional helical structure comprised of two chains. These chains run anti-parallel to one another and are made up of phosphate bases. When analyzed via, mass spectrometry, 13CNMR, 1HNMR, and infrared techniques, the strands of DNA seemed to match the chemical composition of a phosphate and a sugar. Thus, it can be inferred that both a sugar and phosphate make up the backbone of DNA. The sugar was further processed and contained identical functional groups and atomic mass as the deoxyribose sugar molecule. There are four nitrogen bases which make up DNA: adenine, thymine, guanine, and cytosine. Each base seems to have a certain binding preference for another base. Experimentally, adenine, thymine and cytosine, guanine were both found in equal amounts within a DNA sample. Thus the following conclusion can be made. Adenine has a binding specificity for thymine and guanine has a binding specificity for cytosine. It is unknown whether under certain conditions a base will undergo a physical or chemical conformation in order to combine with a different base. For example: In the absence of thymine, would adenine bind to guanine, cytosine, or even itself? What changes would ensue due to these changes? If these changes are made, could the DNA strand be transcribed into an mRNA and translated into a protein? The answers to these questions are unknown. However, this recent advancement in the study of DNA could help other scientist develop techniques to help answer these questions and expand scientific knowledge on DNA and other molecules.
    I also believe another structure of DNA exist as a single stranded chain wrapped around a single axis. The strand is probably composed of alternating anion (negatively charged) and cation (positively charged) bases. The electrical gradient between the two molecules holds the entire chain in place. The interaction of the electrons seems to create a magnetic field causing the bases to probably line up; if they’re chemical composition allows this to be energetically favorable. Another structure that could possibly describe the structure of DNA is a zig-zagged zipper. Each base it tightly zipped together with the other bases surrounding it. Each base is attached to 3 other bases and the middle axis serves as the single backbone supporting the addition of the four bases.

    • I thought it was very interesting when you mentioned a single stranded chain that had alternating negative and positive charges. It is true that the negative charge will attract the positive charge thus holding the bases together. How would you describe the backbone? Would it be strong enough to withstand the multiple attractions and repulsions of the bases? Lastly would the bases have a negative or positive charge naturally? I think that the purines and pyrimidines bases are bases because they have a lone pair of electrons on the nitrogen atom.

    • I really enjoyed reading you post and I thinking you have great input about many of the theories, the only thing that I thought that was a bit odd is the theory of the “zig-zagged zipper” it seems to me that instead of the traditional double helix what you have here is the same thing, but with beta sheets. I was just wondering how would the base pairs go together?

    • I thought your description of the DNA structure was very good. It was very interesting how you mentioned the mass spectrometry, 13CNMR, 1HNMR, and infrared techniques that we are now learning in organic chemistry. It was nice that you analyzed these data that you mentioned when you said that these strands of DNA seem to match the chemical composition of a phosphate and a sugar according to these tests. Also, I think the single structure of DNA that you mentioned which wrapped around a single axis is really good. Especially when you mentioned that theses strands are composed of alternating anion and cation bases. The magnetic field that you mentioned was a nice touch where electrical gradient between the two molecules holds the entire chain in place. I agree that the interaction of the electrons will create a magnetic field causing the bases to probably line up if their chemical composition allows this to be energetically favorable.

    • Your description was very clear, creative and straight to the point. You mentions most of the key points. For the most part I sisnt want to feel like I’m coping off your comment or Ummea’s. You guys took all my word..lol..Good job.

  8. The structure of deoxyribonucleic acid (DNA) is important in the study of biological systems. It is the very essence that determines how a living organism will develop and function. It is found in all dividing cells, mostly likely in the nucleus. It is one of the elements that make up the chromosome and is the carrier of the genes. The structure of DNA is a double helix. Both chains follow right handed helices and the two chains run in opposite directions. X-ray patterns show that the molecule is a long chain that consists of a backbone that is made of alternating phosphates and sugars. The phosphate diester group joins the B-D-deoxyribofuranose residue with a 3’, 5’ linkage.

    Nitrogenous bases are located inside the two strands and are connected to the sugar. They consist of adenine, thymine, guanine and cytosine. The bases are held together by a hydrogen bond. The bases are either purines or pyrimidine. The base pair are assembled in a way to make it most stable. A purine (adenine and guanine) and a pyrimidine (thymine and cytosine) is always pair to one another. When DNA was examined, the amount of adenine was most similar to thymine and the amount of guanine was similar to cytosine. However, the ratio of adenine and to guanine or cytosine was not similar. This means that adenine is pair with thymine and guanine is pair with cytosine

    Linus Pauling and Roberts Corey’s’ model of DNA was a three-chain helix with the bases facing outward and the phosphates in the core. Having three phosphates in the center of the structure would be unlikely because there would probably be too much repulsion. I would propose a model that is a two chained helix with the bases facing outward. The phosphate sugar backbone would be found on the inside of the helix. Both chains will have a right handed helix that joins at the 3’, 5’ linkage. This structure would be helical in order to save space and the nucleotides pairing would be the same. Since the base paring in not in the center the strain would not run in opposite directions. The bases pairing would be the same because of the ratio between adenine and thymine and cytosine and guanine. When this structure of DNA replicates, it would make a template going from 5’ to 3’ from both strands at the same time and then the template will pair with the correct nucleotides and when the phosphate backbone comes together, there will be an exact copy of the DNA. This can explain how DNA replicates so quickly without breaking into pieces.

    • Jason,
      Your response is well thought out and i feel that you put great detail into proposed structure. I find it interesting how you maintained the overall structure of the double helix but placed the bases on the outermost part of the structure. This gives the figure a bit more complexity but at the same time you kept the same basic concept behind how DNA functions. I would only recommend that you add a bit more of Watsons and Cricks wording but overall great piece.

    • I really feel that your post was well researched and thought out. It definitely put many of the important points into perspective on the theory of triple helixes as well as your thoughts on a two chained helix with the bases facing outward.

  9. Despite the assumptions of DNA being portrayed as a complex structure, in reality it is quite simple. The overall foundation of DNA’s existence is solely based on it’s responsibly of being the carrier of genetic information. Hereditary characteristics are passed on from one generation to the next. This type of responsibly can definitely leave your head spinning but overall the structure of DNA is easily understood. In its development of all living organisms, we wish to state that DNA is present in all dividing cells. With contributing facts, DNA itself is said to be a very long chain with two polymers consisting of simple units called nucleotides. It has been made evident that DNA is a double stranded helix, where both spiral strands are secured by hydrogen bonds. The backbone of DNA consists of alternating sugar and phosphate groups. Attached to the sugar/phosphate group is a nitrogenous base. There are four different base types: adenine, thymine, guanine and cytosine, which are classified into two different categories. Adenine and guanine are associated as purines and thymine and cytosine belong to pyrimidines. These bases are positioned in the innermost part of the helix meanwhile phosphates can be seen on the outermost part. Both strands in a double helix are considered antiparallel, where each strand runs in an opposite direction

    It has been taken to consideration that the origin of this structure was proposed by Watson and Crick but there has been much speculation as to whether or not a third helix exists. Although it has not been adequately uncovered with evidence, it is quite understood in what is expressed in previous scientific documents that there is a possibility for a third DNA strand. We wish to put forward in more advancement in technology in the near future. This can only further provide more information and discoveries needed to suggest that a triple helix can be quite possible. In my opinion, it can be assumed that this unknown figure is structured a bit differently as compared to the original DNA body. It’s a bit longer than the expected shape which is said to be 2.2 to 2.6 nanometres. Because the phosphates are positioned on the outside of the helix, we have another linkage of a sugar/base group but can speculate that third helix consist of different base pairing. This portion of the triple strand DNA allow the base members of the same class, such two purines, to cross link with each other causing almost like an X factor effect. It has not escaped my notice that in a double helix this was not permitted due to the lack of room, but because this structure is overall longer and wider due to an additional strand, it provides a sufficient amount of space. The figure itself it still wind around like a railing of a spiral staircase.

    • The idea of the third helix makes a good amount of sense. I like the fact that you explained the size of the triple DNA strand and gave an idea of the space it will have to squeeze into. As technology grows, your theory will definitely be proved or disproved as the DNA experiments continue to improve. Especially if it is found that while there might not be a naturally occurring third strand, a man made third strand can help cure health and mental issues associated with DNA.

    • I feel that this post was very effective in the way you considered the time period. You were talking about DNA as if it was still widely researched about like it was back then. I also like how you used specific numbers like ‘2.2 to 2.6 nanometres’ to describe the size of the DNA. The use of the spiral staircase was also an excellent example of how to imagine the DNA structure.

    • The way you described DNA was so easy to understand but not watered down. You did a great job at describing it in a way that was not to complicated.

  10. Jason Chen,
    Your response is well thought out and i feel that you put great detail into proposed structure. I find it interesting how you maintained the overall structure of the double helix but placed the bases on the outermost part of the structure. This gives the figure a bit more complexity but at the same time you kept the same basic concept behind how DNA functions. I would only recommend that you add a bit more of Watsons and Cricks wording but overall great piece.
    Lauren DiRe,
    Your response was well thought out and you gave sufficient amount of information that helped me easily understand the structure of DNA. I agree with your idea of DNA having a third helix but I couldn’t get an exact visual of how this third strand would be connected in the middle of the outside double heli. Also, what makes the third strand thinner than the other two helixes? Is it because of a different base pairing? Overall, great job.

  11. DNA or deoxyribonucleic acid is usually referred to as the genetic blueprint/ building blocks for all living things, it is consisted of chains of nucleotides built on a sugar and phosphate backbone and wrapped around each other in the form of a double helix and the backbone supports four bases, guanine, cytosine, adenine, and thymine. Guanine and cytosine are always paired up, always appearing opposite each other on the helix, same thing in the case with adenine and thymine. This is important in the reproduction of DNA, as it allows a strand to divide and copy itself because it only needs half of the material in the helix to duplicate successfully.DNA is able to make copies of it, and it also has the coding required for synthesis of RNA, which is another important nucleic acid. DNA also contains sets of base pairs which come together to create the genetic code, determining things like eye color and body structure or phenotypes or the expressed gene. Every cell in our bodies contains DNA which are almost always is identical, with more DNA being produced all the time as cells replicate themselves. Most DNA in most organisms is non-coding, meaning that it does not appear to have any known function basically useless information that is there to take up space and when DNA is changed by a substance known as a mutagen, it may cause health concerns.
    An alternate form of DNA structure that can exist is a structure consisting of 4 helixes if the theory of 3 helixes joining can occur, why can’t 4 helixes join to create a structure considering the fact that guanine-rich sequences can possibly stabilize chromosome ends by creating structures of stacked sets of four-base units, rather than the usual base pairs found in other DNA molecules which is not too farfetched and with the technology we have today we can alter the position and structure making a favorable condition for this structure to exist.

  12. The DNA double helix is the fundamental part of life which supplies genetic information which differs for all organisms. Watson and Crick proposed a three-dimensional structure for the DNA double helix which, if the structure is correct, could suggest a mechanism for its self duplication. The DNA molecule is a long structure which consists of a sugar group and phosphate which alternate to form a sugar-phosphate backbone. Each sugar group has a nitrogenous base attached to it and there are four different bases; adenine and guanine which are considered purines, and thymine and cytosine which are considered pyrimidines. This structure forms a chain and X-ray evidence strongly suggests that there are two chains which are coiled around one another. The two chains are able to remain coiled from the hydrogen bonds which are between two adjacent bases.
    There is no particular order of the base sequence on a strand of DNA; however, the second strand must be in a order where the nitrogenous bases line up with its complimentary base. Complimentary base pairs consist of a purine linked with a pyrimidine by hydrogen bonding. Adenine and thymine are base pair matches, and guanine and cytosine are base pair matches. The process of self duplication suggests that these hydrogen bonds are broken and the DNA strands unwind and separate. The two separate strands of DNA are untwisted from one another which can then undergo a process of transcription and translation.
    An easy way to imagine the three-dimensional structure of a DNA double helix could be equivalent to a twisted latter. The two long parallel poles could represent the chain of base pairs and the horizontal steps could represent the bonds which hold together the complimentary basepairs.
    Gabrielle Barshay- I think that a spiral staircase is a great description for the double helix because it helps us get a better image of what it may look like. I liked your response because it used the same style of scientific writing and it was easier to form a mental image of the structure.

  13. @Kateryna Bushnyak

    I agree with you on your optimism on stronger microscopes and advanced technology on enhancing the image of the third helix. I hope this third helix would hold the key to curing AIDS and Down syndrome, which ruined countless peoples’ lives and preventing them from enjoying life. This cure would help people live healthier, stronger and better.

    @Adedayo Oduwole

    I like how you mentioned using techniques and equipment such as mass spectrometry, 13CNMR, 1HNMR, and the infrared spectroscopy for expressing DNA’s structure. These methods could further the comprehension of what DNA is made up of. Another point of interest is how you proposed that the magnetic field due to the alternating positive and negative charges of the bases contributes to the lining up of the DNA bases.

  14. Deoxyribose nucleic acid is the basis for all genetic differences between organisms. DNA provides the genetic makeup for organisms, which provides and gives way for how an organism functions. The structure Watson and Crick suggested in 1953 for deoxyribose nucleic acid (DNA) gave way to many further scientific discoveries. The structure they proposed was an open, helical shape of two chains which were intertwined around each other. Each of these chains consist of a phosphate di-ester group which join on the 3′, 5′ linkage. The two chains are held together by two base pairs; purine and pyrimidine. The purine and pyrimidine must be binded together by hydrogen bonding. The other complimentary base pairs which bind together are, adenine and thymine, and guanine and cytosine. The helix is joined together when one base pair for one chain binds with a complimentary base pair on the second chain.

    I believe that if there is another structure of DNA that it is going to be different from the traditional helix shape we know of currently. I believe that a third DNA structure could be a single chained structure, however it would fold around itself because the bases would still bind with its complimentary pair. I think the single stranded DNA could give way to faster processing because it would be smaller and less dense than the double stranded molecule.

    @Kateryna Bushnyak:
    I do agree with your idea that with newer developments of technology the new scientific discoveries that come along with it is going to be crucial. I also agree that although we have very good technology now it may not be possible yet for such discoveries because we are not yet advanced enough.

    @Lauren DiRe
    I liked your idea that there could be a third helix within the double stranded helix. I like that you incorporated your idea with the ideas and theories which are already in play.

    • I agree with your statement about the single chain structure. It would make transcription and translation much faster; which would possiblely benefit all organisms. It makes me wonder how would things would occur in the body if the molecule was the way you described; what effects would it have on the development and function of an organism? This opens the door to so many ideas.

  15. DNA (deoxyribonucleic acid) is found in all living organisms. It is made up of four bases, adenine (A), thymine (T), cytosine (C), guanine (G). Adenine connects to thymine while guanine connects to cytosine. However, the purine (A—G) must be balanced by the pyramidine (C—T) to maintain a balance for the double helix shape. There are two strands of DNA that are parallel which are connected to bases. These bases make up the “ladder” of the double helix DNA which are held together by hydrogen bonds. The structure of the DNA ladder is composed of sugars and phosphate atoms that are attached to the bases, which is known as a nucleoside. There are ten nucleotide pairs for every “turn” of the helix. The two strands of DNA that come together to make a double helix are complementary; thus, one side goes from 5’ to 3’, while the other complementary strand goes from 3’ to 5’. On each strand there are structures called telomeres which repeats the bases of the 3’ end of DNA strands, in order to protect the end of the chromosome from destruction. There may also be an Okazaki fragment at the 5’ end of DNA which is made during DNA replication. These Okazaki fragments consist of nucleotides. Okazaki fragment’s purpose is mainly due to DNA being only replicated in the 5’=>3’ strand direction. Therefore, the other end needs to be synthesized with the use of Okaazki fragments which put them together.

    Perhaps instead of having a double helix model of DNA, would it be possible to have more than two strands of DNA combined? Therefore, having a quadruple helix model? As long as two strands that are complementary can come together, is it not possible for four to come together as long as the 5’-> 3’ strand and the 3’=>5’ strand are complementary? This can be researched further through laboratory experiments possibly including the dissembling of a double helix DNA structure.

  16. Deoxyribonucleic acid (DNA) found in all dividing cells, is where most if not all genetic material is found. The structure of the acid is in the form of a double helix which are 2 twisted strands coiled around a common fibre axis with each strand containing nucleic bases. The two strands are bonded together through hydrogen bonds that occur between nucleic base complimentary pairs. The strands are in a right handed position with a leading strand and a lagging strand. In each strand there is a connection between nucleic bases and creates a direction for that strand. Because the second strand must have a specific sequence that is complimentary to the first, it runs in the the opposite direction and thus the two strands become anti – parallel to each other. The leading strand runs from 5’ to 3’ position and the lagging strand from 3’ to 5’. This means that the bonds between the two nucleic bases on the leading strand bond between the 5 carbon on the first base and the 3 carbon on the second base and vice versa for the lagging strand.

    There are 4 nucleic acids found in DNA: adenine and guanine which are called the purines and thymine and cytosine which are called pyrimidines. The nucleic acids can only interact with their complimentary pairs adenine paired with thymine and guanine paired with cytosine. One strand has an apparently random pattern of nucleic acids with the complimentary pairing nucleic acid on the other strand. The nucleic base has phosphate – sugar backbone with the phosphate on the outside of the strand and the sugar inside of the strand causing the outside to be hydrophilic (it likes water) and the inside to be hydrophobic (scared of water). The sugar is attached to one of the nucleic acids pointing toward the middle and hydrogen bonds with its complimentary pair on the opposite strand holding them together.

    But as technology improves, one might find that DNA is not two strands. It can be that DNA essentially is single strand that is forced to fold itself in such a way to fit into the nucleus of a cell and will unfold when it must be copied or transcribed. When it folds itself, it looks like a double helix inside the nucleus and it creates hydrogen bonds with its complimentary base pairs that break with distance. Because of such pairing between the bases, it will only create hydrogen bonds in specific places on the DNA strand and may look like a double helix. This difference between Watson and Crick’s model and my model can clearly be seen when the DNA is replicated. In my DNA, one single strand is being copied while the original model suggested two strands are being created separately and then has a bond between the two separate strands.

    • I like the detail you used to describe the DNA structure and formation in the beginning of your response. However, I was unable to imagine your DNA structure in the last paragraph. I understood how your DNA looked like a double helix but is actually a single strand. You said it was double stranded because it was packed inside the nucleus and was unable to extend to its potential form. After this, I got lost during the last sentence.

      • it means that the it will only fold and create hydrogen bonds with its complimentary base pair that was found by Watson Crick and those folds are what we see as the double helix

      • Darien, I agree with your assessment of Sadia’s post. Sadia, I would also have preferred to see a bit more of a visual explanation of the single helix. I think it is a good imaginary model to work with as it poses many questions in thinking about how it would visually work. For example, how is it that the complimentary base pairs match up if it is originally a single helix? Also, does the single strand have any twist to it or is it straight?

        Again, your description of actual DNA is quite thorough. Think about how you might apply your writing style to the hypothetical portion of your post.

  17. Deoxyribonucleic acid (DNA) has been a very important topic concerning the world as it is the basis for life. It has been questioned about and studied over the last few decades. DNA is a double helix containing a 5 carbon deoxyribose sugar, triphosphate groups, and nucleotides. Within the DNA, there are four types of bases that are commonly found: adenine (A), cytosine (C), guanine (G), thymine (T). These can be simply classified as purines and pyrimidines. A and G are considered to be purines while C and T are considered to be pyrimidines in which they have two rings and one rings respectively. A pairs with T while G pairs with C. Given this, it is viable to say that the amount of A equals the amount of T in a DNA strand. The same concept applies for G and C.

    DNA has a linear backbone and has alternating sugar residues and phosphate groups. The sugars are linked by a 3′,5′ phosphodiester bond. A phosphate group links the 3′ carbon of one atom to the 5′ carbon of another atom. The phosphate group forms the outside of the DNA while the nucleotides are connected on the inside of the structure. With this pattern and the help of hydrogen bonding, the DNA forms a double helix and a duplex. One strand of the DNA runs in the 3′-5′ direction while the other strand of the DNA runs in the 5′-3′ direction making the structure antiparallel. As previously said, the DNA is supported by phosphodiester bonds via the phosphate groups involving the 5′ and 3′ carbons of the sugar backbone. DNA is also supported by hydrogen bonds between the complementary base pairs. However, with these bonds, it does not escape our minds that they effectively support the double helix structure.

    It is in fact very likely that there is another bond responsible for the double helix structure. There is a bond between the phosphate group of one of the DNA strands to the phosphate group of the opposing strand. This bond is not yet named as our current technology is unable to visually see this bond. This bond is not as strong as the tight hydrogen bond but is stronger than the van der waal forces. In fact, it plays such an important role in the DNA structure that with every phosphate association, it twists the molecule a certain degree although accounting for the strong hydrogen bonds in the center of the DNA. In all, this bond creates a DNA structure that looks like an ‘elongated silly straw’. Though more research is needed in this structure, an answer is expected in the next decade as technology advances.

    • Darien, your description of double helix DNA is not only in-depth, your writing is succinct and clear. I felt that your imagined structure was perhaps too abstract for this assignment, in that it focuses more on why it is structured a certain way rather than what it actually looks like. You introduce and conclude this response well, though if you describe something as important or interesting, stop for a second and ask if there is a more precise way of saying that something is important. How is it important? If something is obviously an important research topic, for the purposes of whatever you are writing, consider why it is relevant or what specifically is important.

  18. In order to understand the three-dimensional structure of DNA, it’s convenient to think of DNA as a ladder-like molecule with a very regular structure. The hydrogen bonding between base pairs is responsible for forming the regular structure with antiparallel strands. This simply means that the 5′ end of a strand is paired with the 3′ end of its complementary strand and vice versa.
    The double helix arises from the chemical and structural features of its two polynucleotide chains. Because these two chains are held together by hydrogen bonding between the bases, adenine (A) with thymine (T) and guanine (G) with cytosine (C) on the different strands, all the bases are on the inside of the double helix, and the sugar-phosphate backbones are on the outside. In each case, a bulkier two-ring base is paired with a single-ring base. A always pairs with T, and G with C. This complementary base-pairing enables the base pair to be packed in the energetically most favorable arrangement in the interior, which is hydrophilic, of the double helix. In this arrangement, each base pair is of similar width, thus holding the sugar-phosphate backbones an equal distance apart along the DNA molecule.

    • I like your description of the structure of DNA. It is very easy to understand even if you don’t know much about DNA. Even when you go further into depth on purines and pyrimidines understanding what you mean is easy. good job.

  19. Deoxyribonucleic Acid(DNA) is a nucleic acid that contains genetic development and functions that is found in every cell on earth. DNA is found mainly within chromosomes and it takes on a role of long term storage information and DNA segments carry proteins and RNA molecules that have genetic information called genes. As we all know DNA usually does not exist as a single molecule but has two strands that intertwine in a shape called double helix. The double helix is stabilized by hydrogen bond that is between the bases. The four bases found in DNA are Adenine, Guanine, Thymine, and Cytosine. These four bases attach to the sugar phosphate to form the complete nucleotide. A nucleotide only has three parts, a phosphate group, 2-deoxyribose and an organic base. The DNA strand that shows the direction of these synthesis are called five prime and three prime (or 5’ and 3’)
    Like Pauling and Corey I would make the triple helix structure as well because I believe the structure isn’t impossible as some might have said. The flaws mentioned by Watson and Crick: Negatively charged phosphates will repel each other and the other problem is that the three-chain structure would not stay together. So instead if the phosphates near the axis were placed somewhere else to stop the repelling the structure would able to hold. As I was reading this article about how the triple helix’s structure impossible to form, I remembered about reading an article or some sort about how the triple helix was possible. After some research I found that the article about the structure of triple helix does exist. Basically a triple helix is a triple stranded DNA where three oligonucleotide wind around each other to form a triple helix. This structure is different from the double helix because one strand binds to a B-form DNA double helix through Hoogsten hydrogen bonds (a variation of base-printing in nucleotide acids)

    • Ummea Urmi:
      Your work in the DNA description seems to be very clear. When I read your post, I was able to understand most of the materials you explained. Very nice job!
      John Hang Leung
      The triple helix that you mentioned in your post, I’d have to say I completely agree. As I’ve done my research the third helix is possible and the DNA structure will not fall apart as the other scientist might have proved.

  20. Deoxyribose Nucleic Acid is a fundamental unit of life, it composes of all of our genetic material which then codes for the proteins causing and creating bodily reactions. Without such a grand structure humans would not be so complex. DNA is considered to be in the shape of a double helix, which means it has two strands intertwined with each other. These two strands are connected by the complimentary nitrogenous bases; Adenine which binds only with Thymine and Guanine which binds only with Cytosine. These nitrogenous bases are bonded together by hydrogen bonds. Adenine and Guanine are purines, while Thymine and Cytosine are pyrimidines. In the article it states how DNA has a backbone which consists of alternating sugar and phosphate groups which are then attached to one of the four nitrogenous bases. The single strands on the double helix are said to be anti parallel due to the 3′ to 5′ phosphodiester bonds between the phosphate groups.

    DNA has always known to be the double helix molecule, with two strands wrapped around each other, but what if that wasnt the case. But, what if DNA wasnt that standard helix, but rather a disk or just a loop. Something that could be transported or compressed much easier, but scientists have always inquired about the wonders of the helix and why it makes it so great.

    • I liked how in your speculation you didn’t just “speculate”, you actually provided enough information as to what it could be even though you don;t know the exact answer to that question.

    • Devang, I think you are on the right track in terms of your description of real DNA, but the description of the hypothetical DNA structure seems to be lacking. Your second section seems a bit too short. Your hypothetical DNA structure is quite interesting and deserves a bit more elaboration. If you had to say just as much about the imagined structure as the real one, what would you say? Just looking at the length of everyone’s posts, you’ll notice that most people seem to be spending much more time describing real DNA structure than their imagined structure, and I would recommend everyone avoid losing momentum in the second half of their response.

      I would also recommend to double check sentence structure and punctuation, just for the sake of clarity.

  21. The deoxyribose nucleic acid otherwise known as DNA is in the shape of a double helix, where two phosphate sugar chains make up the backbone of the structure. The backbone of the structure is constructed from sugar and phosphate molecules which are right handed and anti-parallel in direction. On the inside are the Nitrogenous bases. The whole thing is held together by hydrogen bonds. There are four different nitrogenous bases that make up the interior of the helix which are non-polar and hydrophobic : Adenine, Thymine, Cytosine and Guanine. These bases are selective as to which other base they connect with where they complement each other. Adenine always pairs with Thymine and Guanine always pairs with Cytosine.

    While I was reading some of the alternate shapes for the DNA double helix i found it to be a little monotonous. Not that this is not dis proven yet, it also has not been proven which makes it a known unknown. I do understand that in the future more advanced technology could prove this or any other shape. While reading all the numbers of people saying triple helix’s I said, why cant there be four? The separate strands of the phosphate sugar backbone will be anti-parallel to the ones directly next to it while keeping the bases between the different strands held together by hydrogen bonds.

    • I agree, it’s very possible there could be four as well. I believe that four strands seems more logical than 3. The base pairs would be more even that way. It creates a more structured backbone for the pairs. It’d be a richer sequence.

      • I also agree. i was actually think of that myself. I think four strands would give the DNA molecule more of a balanced feel. I feel like it would just give it more balance in everything especailly replication and other such stuff, if there were three strands replication might be awkward.

  22. The three-dimensional structure of deoxyribose nucleic acid (DNA) is much more than regular double helix. The DNA double helix is structured with the phosphate group, the sugar backbone group and also a nitrogenous base. The phosphate group is on one side of the sugar group; and on the other side it is attached to a nitrogenous base. There are four different bases: adenine (A), guanine (G), cytosine (C), and thymine (T). It is the nucleotide bases that make each of the DNA units different from each other. The hydrogen bonds between these bases hold the two single strands DNA together where adenine (A) only binds to thymine (T) with 2 hydrogen bonds and guanine (G) binds to cytosine (C) with 3 hydrogen bonds. Adenine and guanine are both purines and thymine and cytosine are both primidines. A purine must pair with a primidine in order for the bonding to occur. The two strands of DNA run anti parallel, one goes from 5’ to 3’ and the complementary strand is from 3’ to 5’.

    Since the molecule is an open structure, there are spaces between the two strands of DNA. The DNA can take in other forms and it is possible that there is a third strand of DNA involved. The third strands of DNA could be in the helical form, making the double helix into a triple helix, where the nucleotide bases are bonded with two of the three strands in an alternating manner just like “hair braiding”. The strands of DNA will be alternated with different pair of nucleotide bases. Once the two strands are formed into a double helix, the third strand will go in between the double helix and form with one strand of the helix, which forms another double helix, and the formation will continue.

    • I think this is a good post but needs a little revision in terms of sentence structure in the second paragraph. Think about how you might break down your ideas/explanation further, in order to keep the reader’s attention and clearly depict your hypothetical DNA structure.

  23. Deoxyribonucleic Acid, otherwise known as DNA is a nucleic acid responsible for the genetic makeup of a living being. It’s often referred to as the ‘genetic blueprint’ because it contains all the instructions for all parts of a cell. DNA is known to carry genes, or genetic information, in each segment of its sequence. The sequence of DNA is a unique one in that it follows a double helical, right-handed spiral structure. It contains two long helical chains that consist of polymers. These polymers hold repeating subunits called nucleotides, and the chain falls back onto backbones; which are phosphate and sugar groups bound together by an ester bond. This gives the DNA structure a “winding staircase” look, because they are anti-parallel. Each nucleotide is composed of a base, a phosphate and a sugar; while each sugar contains four different types of bases. The bases are stacked on top of each other. The genetic information is carried in these nonpolar bases, known as, adenine and guanine, which are purines, and cytosine and thymine, which are pyrimidines. One must always remember that the adenine bases and the number of thymine bases equal each other, while the number of guanine bases and the number of cytosine bases equal each other. Thus, the number of purine bases must equal the number of pyrimidine bases.

    Other than the DNA structure that Watson and Crick show here, there are speculations that other types of DNA structures do exist. The possibility of a third helix is very high, in that this specific structure seems very wide; a little too wide. There is a possibility that there is enough room for a third strand, in which different base pairs can be found. However, the possibility of this can only be proven with more technological advancements in the area of science. Hopefully, the scientific world can answer our inquiries about this in the near future.

    • This is truly a great response to the article, and i was really able to pick up on the style of writing you incorporated based on the article. As many people have posted about the third strand, i think that would be a highly plausible idea especially with the great advancements in technology as you stated, but as Prof said; there actually might be a DNA with a third strand out there

  24. DNA is a nucleic acid that contains genetic instructions that are essential to the growth and performance of all living creatures. The main function of this nucleic acid is to store all different types of information that pertain to a certain organism. It is thought of as the perfect design of a genetic information system. DNA is responsible for the instructions to make other components of cells, such as RNA and different kinds of proteins. With such a major role in the coordination of life, it is proper to assume that its structure would be nothing less than complex.
    DNA consists of two long polymer chains that twist to form a double helix, which are made up of nucleotides. Nucleotides are made up of nitrogenous bases that can either be purines or pyrimidines, a pentose sugar and a phosphate group. The purines consist of the bases on adenine and guanine, while the pyrimidines contain the chemical bases of cytosine and thymine. It is interesting to point out that in the DNA structure, each purine matches up correctly with a pyrimidine. This is because a purine-purine matchup creates a structure larger than a purine-pyrimidine connection that would disrupt the overall helical structure of the molecule. A pyrimidine-pyrimidine linkage would also disrupt the structure of DNA, but the reason behind this would be because this particular relation would create a smaller structure.
    The two sugar-phosphate backbones operate in opposite five prime to three prime directions from each other, a collection referred to as anti-parallel. These backbones are on the outside of the helix, making them hydrophillic, and the nitrogenous bases are paired in the interior of the helix, making them hydrophobic. These two polymer strands are held together by hydrogen bonds between paired bases and by Vander Waals interactions between the bases. In DNA, adenine, a purine, matches up with thymine, a pyrimidine; while cytosine, a pyrimidine, connects with guanine, a purine. This feature of DNA enhances its vital role in genetics, the complementary aspect of each strand allows for the predictability of the new daughter strand.
    Even though DNA has a helical structure, there have been other proposed structures. One structure that I propose is a circular structure, similar to the shape of a plasmid. The arrangement of the phosphate backbone and the nitrogenous bases would resemble that of the helical DNA structure, with the hydrophobic backbone on the outside and the hydrophilic bases pointing inward. The phosphate group would be the shell, and the bases would be the core. The core would be connected to the shell by special bonds, different from the phosphodiester bonds that hold the phosphate backbone. These bonds may most likely resemble hydrogen bonds that connect the bases but a bit stronger to hold together what appears to be a ball shaped figure. However, unlike the helical form of DNA, the base pairings would be unusual. The structure would be engulfed with purine-purine linkages making the DNA structure very large. Additionally, pyrimidine-pyrimidine connections would be mostly closer to the core making it the tightest part of the DNA, where everything is compactly kept together. While this structure of DNA may possess a greater size than the helical DNA, it could be in the realm of possibility of structures.

    • Good job at being a little more creative with the dna structure that you thought of. A lot of other people went along with the third helix idea stated in the paper we read.

    • Michael– I agree with John that your hypothetical DNA structure is very creative. I think that you take it a step further than simply restructuring it-you change the chemical properties. I would take another look at your description of actual DNA. If you were to revise, consider avoiding any wordiness or redundancy. You introduce this response very well, but you might be able to say more in less words, or potentially cut out unneeded words.

      Good post.

  25. Deoxyribose nucleic acid (D.N.A.) is known as the genetic structure that houses genetic material used for a variety of functions relating to life. D.N.A. is made up of two helical chains that are coiled around each other in opposite direction (anti-parallel) . Previous X-ray experimentation had allowed a further analysis of the molecule; this resulted in the discovery that the molecule is a long chain that contains a backbone made of phosphates and sugars groups (alternating). In addition to this concept, each chain consists of phosphate diester groups which join with 3′, 5′ linkages. Within this helix, nitrogenous bases are located on the inner regions of the helix and are held together by hydrogen bonds. The nitrogenous bases are connected to several sugar bases which are adenine, guanine, thymine, and cytosine. Adenine and guanine are classified as purines, while thymine and cytosine are classified within the pyrimidines category. Purines adenine and guanine can only form bonds between pyrimidines thymine and cytosine (adenine with thymine, and guanine bonds with cytosine).

    It has come to my attention that since their were several different types of DNA structure ideas, it is possible to have a quintuple helix structure. Each individual strand would generally be comprised of the similar backbone, but instead of housing the sugar bases on the inner sections of the structure, they would be located on the outside. In addition to this, the structure would still connect at the proper 3′ and 5′ sections, thus making it possible to exists if the conditions were met. With the proper experimentation, it is possible to test for the possibility that this structure is capable of existing.

    @ Grace: I believe your interpretation of the description of the the DNA structure was well presented. I especially enjoyed your use of the Okazaki fragments.

    @ Ling: I would have preferred for you to have had explain the concept behind the guanine-rich sequences stabilizing chromosome ends by creating structures of stacked sets of four-base units. It would have portrayed a stronger concept towards your readers. As for your description of the DNA structure, I enjoyed it and believe it was on point.

  26. To Mike: Your structure seemed very well thought out. The plasmid shape DNA in my opinion was a simplistic and idealistic shape to use as a way to describe the shape of your DNA. I found the idea of a pyrimidine to pyrimidine base to be very unique and the compactness of your DNA molecule to be very useful in the super coiling of DNA.

    To Devang : Your DNA molecule seems very simple and because its a single strand molecule there would probably less errors during replication.. The disk shaped in my opinion is very similar to a shape of a plasmid.

  27. The structure of DNA can be best described as a double helix with nucleotide bases attached to one another by hydrogen bonds. The structure is same in all in all species but the number of nucleotide bases varies depending on the type of the nucleic acid and organism. The base adenine is complementary to thymine and guanine is complementary to cytosine and hydrophobic. This means the ratio distribution of adenine and thymine nucleotide bases are the same. This also means guanine and cytosine bases are equal in number as well. The backbone of the double helix is a 2-deoxyribose sugar and phosphate molecules. The DNA molecule runs in a 5’ to 3’ direction and is considered to be anti- parallel. The leading strand runs from 5’ to 3’ direction. The lagging strand which is complementary to the leading strands runs from 3’ to 5’ direction. DNA is essential in living things and is important passing along genes from one generation from another. It also plays an important biological role in directing the synthesis of mRNA in organisms and is a faithful copy of DNA.
    My structure of DNA varies significantly from Watson and Crick The final proposed structure can be best be described as a twisted Y shaped helical ladder structure molecule that is held together by hydrogen and covalent bonds that contributes to its rigidity and shape. The base pairs consist of 4 nucleotide base pairs which are adenine, guanine, cytosine, and thymine. These bases pair guanine (purine) with cytosine (pyrimidine), and adenine (purine) with thymine (pyrimidine). There are approximately 7.4 x 10^8 nucleotides in this Y shaped DNA structure and about 12 nucleotide pairs per helical turn. The length of a nucleotide is approximately 5 A (Angstroms) and the sequence and DNA length is dependent on the animal species. The nucleotide bases which are adjacent to one another are approximately 10 A apart. The nucleotide bases are bonded to one another by covalent bonds but bonded to the sugar phosphate backbone by hydrogen bonds. When super coiled into a compact chromosome it resembles a shape of a star.

    • to ian: I find the deviation from watson and crick’s original interesting especially after you explained it so well. As for your ‘Y’ structure, what happens at the juncture at the center of the Y? I’m just curious.

  28. @Lauren
    I like your description of DNA, giving an accurate and detailed explanation its different features. I can see the possibility of a third strand. According to the papers written by Watson and Crick, DNA is a very open molecule. I like the use of speculation in your essay, where you left me at least with the strong belief that a third strand is possible, with the use of more advanced technology.
    @Ian
    I admire your structure of DNA. Your description was well thought out, painting a clear picture in my mind of DNA. I like how your structure is similar to the Watson and Crick model, but is extremely more complex. Your description is enhanced by the numbers you have added. It allowed me to honestly believe in your structure. The fact that your structure, when compacted, would resemble a star, made me appreciate its overall form and complexity

  29. DNA is a molecule whose structure is made up of two strands bound together in a double helix by molecules known as bases. The base is consisted of three parts: a sugar molecule which has a nitrogenous base bonded to its 1’ carbon and a phosphate group bonded to its 5’ carbon. There are two types of bases: pyrimidines and purines. Purines are adenine and guanine. Pyrimidines are cytosine and thymine. They are usually abbreviated by the first letter of their name. Uracil is the only pyrimidine base that appears only in RNA molecules. According to experiments, the bases are complementary to one another. Base A always bonds to base T. Similarly Base G always bonds to base C. If you know one base, you can find the other.

    Hydrogen bonds connect these two bases together. Bases A and T has two hydrogen bonds. Bases C and G have three hydrogen bonds. Along each strand of the double helix, the bases are bonded together by the 5 and 3 carbons of the nucleotides by the phosphate groups. Since only two out of the three oxygens are used in the phosphate group, the backbone has a negative charge due the remaining unbonded oxygen. The two strands are antiparallel which means they run in opposite directions. If one strand starts with a 3’ carbon and ends with a 5’ carbon, its complementary strand will begin with a 5’ carbon and end with a 3’ carbon.

    Humans are susceptible to foreign bacteria and other viruses because the body doesn’t have the strong immune system or certain proteins to fight the disease. Some illnesses don’t even originate from the outside world such as genetic diseases which are known to be nearly incurable. Maybe the third strand of special DNA may assist in this challenging problem. The third strand wraps around the whole double helix like a plastic covering around a book, bonding with the only one negatively charged oxygen in the phosphate groups. Chemical bonding is the purpose for each atom to have an octet or at least be neutral. This third strand provides the stability to the double helix. Since this third strand stabilizes the double strand DNA, maybe by studying it could help find the solution to genetic diseases. As technology advances, maybe there will be a way to diagnose the problem and fix it before the baby is even born.

    • Your initial description of the DNA molecule was very detailed yet simple to read. If I didn’t know much about DNA reading this post would have been a very nice way to introduce myself to it.

  30. Many scientists suggest that Deoxyribonucleic acid (DNA) is the back bone of all biological interest. Its major function is to maintain the balance of what leaves the nucleus as mRNA to eventually become a protein and act out its purpose to contribute to an organisms’ survival. DNA consists of two nucleotides, with backbones made of sugars and phosphate groups joined by ester bonds. These two strands run in opposite directions to each other and are therefore anti-parallel. Attached to each sugar is one of four types of molecules called bases. It is the sequence of these four bases (A), adenine, (T), thymine (C), cytosine (G), guanine along the backbone that encodes information. The base pairs match up as follows A-T and G-C because that’s how it fits due to hydrogen bonding in the 5’-3’ linkage configuration of the structure. This research of Watson and Crick in 1953 when they were first proposing the notion of the structure of DNA suggests all these things and many more.
    A structure for DNA was proposed by Pauling and Corey before Watson and Crick. They proposed a triple helix but their model failed to predict the structure of DNA. In their triple helix model, the phosphates formed the helical core with the bases pointing outward. Logically speaking, these bases are negatively charged, not only that but so is the overall surrounding in this predisposition. In other words, this structure will always repelling itself from the outside and will eventually break apart because of its instability. With this one is led to believe that this notion is flawed
    In my DNA ‘structure’ I propose the following: Let’s focus the 3’-5’ linkages on the major chains first. I still think a similar structure to Pauling and Corey could work except for the exposed bases. So I think that a stand can possibly have a triple helix structure. The glue of this product will be the phosphodiesterbonds on the beta sheet and the main support would be two antiparallel chains from the original mix and an extra chain that pulls on the OH groups. Now I know it sounds weird but this kind of structure can expand the internal sheet to make the 3-D structure look something like a twisting prism.
    I am well aware that this might not work as it might collapse in on itself because the inner beta sheet may become more electronegative than the outer chains which could attract disaster because of instability, but I still see it as a possibility to even go as far as a quadruple strand because that beta sheet just seems to leave room for error despite its hydrophobicity.

  31. DNA serves as an important tool in the study of various biological sciences. DNA contains all the genetic instruction applicable to the development of an organism. It is known to be located in the nucleus of every cell but it’s also found in the mitochondria. The structure of DNA is in the form of a double helix that consists of a sugar-phosphate di-ester which makes up the backbone (outside) of the double helix. The bases, Pyrimidine and Purine, make up the inside of the double helical structure. There are four different bases; adenine (purine), guanine (purine), cytosine (pyrimidine), and thymine (pyrimidine). The bases purine & pyrimidine bind together through hydrogen binding, which holds the chain together. The bond order would be Adenine with Thymine & Cytosine with Guanine forming base pairs. The sugar-phosphate and base is known as a nucleotide. One helical chain runs in a 3’-5’ direction while the other runs in reverse. The helical chain of DNA consists of about 2-3 million bases which vary in sequence. The sequence of the bases determines the attribute or function of the organism.
    I believe DNA isn’t always a double helix that Watson and Crick described in the mid 1900s. There is another structure that DNA forms other than the double helix that we have come to know and learn about all these years. I believe the DNA helical chain flattens out to form two parallel chains side by side, somewhat similar to the structure of an extension ladder (http://professional-power-tool-guide.com/wp-content/uploads/2008/10/extension-ladder.jpg). This would occur before DNA would interact with mRNA (translation). Rather than the DNA disconnecting one base at a time, it would disconnect all at once in this structure, making translation much faster.

    • @ marvin: that’s a pretty rigid structure you’ve come up. It’s great also because of the transcription but wouldn’t that mean that more of the stucture would be left behind because of easier splicing during the mRNA sequence?

      • I like the way you explained the dna structure in simple and easy to understand manner. The structure that you came up with also seems very plausible

  32. Michelle Zur
    Dr. Mark Gillespie
    Pharmocogenomics
    February 16, 2011

    Watson & Crick DNA Description

    Watson and Crick have a very descriptive and organized way of illustrating a clear picture of their idea of the DNA molecule. The two scientists start with a pretty general description of the molecule, such as the shape and general orientation of the different parts of the DNA molecule. Then, however, they begin to go into much further depth about the distance of each structure, such as their idea of each phosphorous atom being 10 A from the fibre axis. Then they go further into almost every aspect of the structure, such as the order and combination of the base pairs and what the space between and within the molecule is filled with. They have a very organized explanation. It seems like it has a general order to it. It goes from less complex to more complex as well as going from the structure of the helix, to the bonds between the two strands, and finally to the nitrogenous bases themselves.
    My structure of DNA can be found in the nucleus in its natural folded state. The DNA structure naturally occurs in folded sheets of DNA. When unfolded the DNA is a flat molecule that has two parallel strands with nitrogenous bases in the center of the two strands. When looked at from a frontal view the strands look wavy. This is caused by the different sizes of the nitrogenous bases. On the crests of the strands two purines are located, connected by hydrogen bonds. On the troughs of the strands there are two pyrimdines, also joined by a hydrogen bond. Because the two purines are separately longer than pyrimidines, when combined, they are significantly longer than two pyrimidines. This causes the wavy form of the DNA molecule. The stands are made up of alternating phosphate groups and deoxyribose sugar. The folding in the DNA molecule is caused by special attractions between the phosphate groups and the sugars on the strands. These attractions occur on every twelve nanometers of DNA. Therefore, DNA in the nucleus is found in twelve nanometers long folded sheets.

  33. It has been found through research that that DNA is a very intricate and complex structure. DNA, which is deoxyribonucleic acid, is a rather long molecule, that is replicated and inherited. DNA is made up of two long polymers of simple units called nucleotides. Nucleotides are comprised of a base, a sugar and a phosphate. The DNA bases are guanine, cytosine and thymine. It has been established that the bases pair up with one another as folllows: adenine with thymine, and cytosine with guanine. THerefore, the bases are commonly referred to as base pairs. There exists bonds between these base pairs that are hydrogen bonds.
    With regard to the structure of DNA, it can be described as a double helical structure. The nucleotides are arranged in two strands which manifest themselves as spiral strands. It would help to visualize the structure of DNA by forming a mental picture of a ladder. The rungs of this ladder are formed by base pairs, and the vertical sides of the ladder are formed by the sugar and phosphate molecules. The strands are known to be anti parallel because they go in opposite directions.
    One can also visualize a slightly diverse structure for DNA. Such structure might have a single coiled helix. The bases would be randomly located and no pairing would occur, nor would they run in opposite directions from one another. The backbone of this structure would not be deoxyribose sugar and phosphate molecules. Each of the single pairs contains all possible bonds and would be a more efficient molecule.

    • Your description was pretty good clear. i can easily picture the structure in my head. The structure you thought of would be very interesting. I wonder “How would things change since the bases don’t bond and that they are randomly located along the chain?”

  34. I would like to propose a three dimensional structure of DNA. This structure involves innovative features which serve to provide substantial biological importance. American biochemist Linus and Corey suggested a three-dimensional structure of DNA based on molecular distances and bond angles. Their structure is depicted as three intertwined chains with bases on the outside and the phosphates in close proximity to the fiber. I deem their model as incorrect for two plausible reasons. Firstly, it is not probable that the free acid is the material that gives the x-ray diagram because it does not provide enough evidence to hold the structure together. Which is why I believe the material that gives the xray diagram is the salt. Secondly, the distances made by the van der Waals seem to be too small. Furthermore, a similar structure with three intertwined chains has been proposed by Fraser. His model depicts the phosphates being on the outside and the bases on the inside, linked by hydrogen bonds. However, his explanation for his model is rather vague which does not provide me sufficient cause to remark on it. Although my suggestion of the three dimensional structure and function of DNA has relied heavily on the work of other scientists, it is certainly quite different. The structure I would recommend you to consider is a double-stranded helix, with the two strands connected by hydrogen bonds. The two chains are right handed. The DNA double helix is anti-parallel, which means that the sequences of the atoms in both strands run in opposite directions. Moreover, the 5’ end of one chain is paired with the 3’ end of its complementary strand. Therefore, nucleotides are linked to each other by their phosphate groups, which bind the 3’ end of one sugar to the 5’ end of the next sugar. Essentially creating 3’,5’ linkages. This vaguely resembles the model proposed by Furberg, in which the bases are on the inside of the helix and the phosphates being on the outside. Nonetheless, novel idea of the model is in regards to how the two chains are connected by the purine and pyrimidine bases. They are joined together in specific pairs; adenine (purine) with thymine (pyrimidine) and guanine (purine) with cytosine (pyrimidine). Therefore, it is plausible to immediately determine the sequence of a chain if the sequences on the complementary chain are given. I also believe that it may not be possible to create this model with a ribose sugar instead of the deoxyribose sugar because the van der Waals distance will be too close due to the extra oxygen. Moreover, the outer edges of the nitrogen-containing bases are vacant for potential hydrogen bonding. The structure I have described and proposed give sufficient reason to suggest a probable role in the replication and expression of DNA. Further full details on the vital role of this structure will be published in the near future.
    I would like to suggest a new structure for DNA. In 1953, Watson and Crick suggested a double helix structure, connected by hydrogen bonds, with the two chains held together by the purine and pyrimidine bases. However, I find this to be unsatisfactory. With extensive research, I am proposing a new structure that vaguely resembles that of Watson and Crick. The Watson and Crick model is made up of two chains. However, I believe that the structure of DNA is a single helix. This single helix closely resembles a slinky. It is also shares the features of a slinky in that it can coil very tightly as well as stretch out. The single chain is coiled around an axis. Like what Watson and Crick proposed, there are four bases. They are joined together in specific pairs; adenine (purine) with thymine (pyrimidine) and guanine (purine) with cytosine (pyrimidine). Although, all the bases are on the same chain, they are attracted to one another based on their direction around the axis. The purine bases are located on the chain on the left side of the axis and the pyrimidine bases are on the same chain but on the right side of the axis. This is a more accurate description of DNA than what Watson and Crick proposed, because at the end of the structure the strand makes a hairpin loop, further proposing that there is only a single helix around the axis.
    @Jason Chen- I thought Jason did a good job in his blog in that he incorporated scientists from the past such as Pauling and Corey and described why their idea is wrong and why his is a better idea than theres. I felt that this was an important criteria for our blog assignment in that it incorporates speculation. He speculated why they were wrong, and why he was right. I also felt that he did a good job in describing his structure. He provided sufficient reasoning such as when he stated “This structure would be helical in order to save space…” and “This can explain how DNA replicates so quickly without breaking into pieces.”

    @ John Beck: I liked that even though other scientist claimed the triple helix structure as impossible, he still did not assume them to be correct in their predictions just because they are scientists and have published work. He still kept an open mind and did research on triple helix structures. I think this is an important trait to have as a scientist because speculation is in fact what drives science forward.

    • “I think this is an important trait to have as a scientist because speculation is in fact what drives science forward” I really agree. It seems odd to say, but it is good to be wrong sometimes. You know you are pushing your ideas forward this way.

  35. It has been previously proposed that DNA is a polymer composed of nucleotides. These nucleotides come together into helical chains that intertwine to form the shape of a double helix similar in structure to a spiral staircase. Each has a phosphate sugar backbone and base that holds these chains together. The bonding of the backbone is antiparallel, meaning the nucleotides in one strand are opposite in direction to the other and therefore have a direction. The interior of the double helix consists of bases stabilized by hydrogen bonds. These bases are adenine(A) ,guanine(G)(purines) cytosine(C) and thymine(T)(pyrimidines). It has been found that each base from one strand is specific for a base on the other strand, A only binds to T and G only binds to C. This is known a complementary base pairing. It is believed that these base pairs hold the necessary code needed for replication.
    I would like to respectfully disagree with the above suggested structure. I propose that there is a triple helix structure. This triple helix involves a third heterogeneous chain that has both purines and pyrimidines face outward. It consists of a phosphate sugar backbone that increases stability but also makes the structure much more rigid. Watson and Crick talk about an imaginary axis that the double helix structure revolves around, well this is literally the physical axis that supports the double helix.

    • I liked how you described not only what you proposed but a reason as to why this phenomenon would happen. Also explaining the reasoning behind your argument before you gave it to the reader was helpful.

  36. Deoxyribose nucleic acid (DNA) is accountable for the genetic material in humans. Although the structure for DNA has been proposed previously by Watson and Crick as a double helix that where two polymers run in opposite directions (3′-to-5′ and 5′-to-3′) and the deoxyribose sugar is the hub of this numbering system — the 3′ carbon contains a hydroxyl group and the 5′ carbon has a phosphate. This structure, although right in the polymers running in the opposite direction, is not correct in the shape of DNA for reasons I wish not to discuss.
    I propose a different structure for DNA. This structure is composed of complimentary bases running parallel to each other joined tightly together side by side. I have made the assumption that ones side of DNA called alpha strand is composed of complimentary bases adenine (A) and thymine (T) stacked one after the other correspondently. One end of the alpha strand contains the the 3′ carbon with a hydroxyl group and the other end contains the 5′ carbon with a phosphate. The other strand, beta strand, also contains the 3′-to-5′ direction at the end of the strand but have different complimentary bases. Beta strand has cytosine (C) and guanine (G) bases that also stack together to form a long chain. The alpha chain has a slightly negative charge while the beta shape has a slightly positive charge. The charges are what bind the two chains together.
    It is not without notice that the charges in beta and alpha chains could be responsible for the copying of genetic material. Since the charges are strong enough to hold DNA strand together but not strong enough to not be able to be broken apart. The full details of this suggestion will be published in another article.

    • Valentina- I wonder why you say “for reasons I wish not to discuss”? For scientific writing, this seems a bit vague. Or, as this idiom is connotative of something stressful or secretive, perhaps it would have been more appropriate to say, for example, “reasons outside the scope of this paper,” which would simply imply that those reasons are too complicated or irrelevant. However, I do like how you spend more time discussing the imagined structure than the actual structure. This puts the focus, hypothetically, on new and continued research, rather than the reiteration of old news. It is also interesting that you are moving towards writing as if this were actually in a published article (“..will be published in another article”).

  37. Watson and Crick were the first people to come up with the correct structure of DNA, others before tried and had many differnet ideas what it looked like. Watson and Crick found that it was a double stranded and wound around a central axis making it a double helix. The bases of the DNA strand are attached to each other and the phosphate backbone. The nitrogeneous bases are always attached in the purine to pyrimidine matter as adenine always pairs with thymine and guanine always pairs with cytosine.
    My DNA structure would be different then the actual one. Mine is wavy and can be described structure wise as likea rollercoaster. The bases are still attached adenine to thymine and guanine to cytosine and all are attached to the phosphate backbone. The wave and rollercoaster like form allows DNA to be replicated very easily and also easily fits inside the nucleus. This also allows the DNA molecule to be used in all kinds of expierments with no problems.

    • John– You have a creative hypothetical strand but overall this response feels a little rushed. I’m not really talking about the length of it, but this sense that it could be a bit more concrete or in-depth, (which would contribute to length of course). The roller coaster visual is a very concrete metaphor, but I feel like I still only have a vague understanding of what it looks like or what it is made of. Does it still have only two helices? Otherwise, the preciseness of this short response is something to consider as valuable… sometimes you can say more in less words.

      The first sentence feels a little choppy; consider revising to avoid a run-on sentence and to make it clear to the reader what you will discuss in your essay.

  38. Deoxyribose nucleic acid, or DNA, is an important molecule that serves the foundation of the complex structures we are. The much researched and understood structure of DNA describes it as two helices joined by hydrogen bonds. Each strand is composed of a sugar phosphate backbone that is attached to bases. The bases are on the inside of the helix and phosphates on the outside. The interior of the deoxyribose nucleic acid is composed of a series of four nitrogenous bases: adenine, guanine, thymine, and cytosine. Unlike the backbone of the molecule, these bases are hyrdophobic. The orientation of the molecules backbone is built from deoxyribose sugar and phosphate molecules in a constantly alternating fashion; the backbone is both polar and hydrophillic. The four bases are complementary to each other, for example, adenine joins with thymine and guanine joins with cytosine and there is hydrogen bonding between these paired bases. Housed inside of cells, DNA is organized into cellular structures known as chromosomes. DNA yields the related molecule RNA by the process of transcription.
    There is probability that a third helix may in fact exist. Being such an incredibly complex molecule unique to each individual, a third helix may confer greater variability, an important feature in such an important biological molecule. The greatest problem to surmount is the location of this phantom helix, we need the science and engineering to locate this molecule.

  39. Deoxyribose nucleic acid, more commonly known as DNA, is an essential part of organisims. it is the make up of their very being and transfers genetic information. the stucture of DNA is quite simple. it is two long linear antiparallel polymers bonded together by hydrogen bonds. the polymers starts with 3′ and end at 5′. being that the structure is antiparallel the 3′ is connected to the 5′ of the other strand and end with the 5′ connected to the 3′. the shape of DNA is called the double helix. the backbone is made up of deoxyribose sugar and phosphate. the back bone is hydrophillic and polar. this backbone is attached to four different nitrogenous bases adenine, guanine, thymine, and cytosine. these bases are very specific; adenine to thymine and guranine to cytosine. these bases are hydrophobic and non-polar. these DNA strands are found inside the cell of an organism.
    for my structure of DNA i would like to propose the stucture of a DNA double helix ring. the ring will be just like the watson and crick double helix but at the 5′ and 3′ end it will connect with the 3′ and 5′ end. where the ends meet is where they would detatch and then copies would be made. they would also detatch if they needed to get to different parts of the cell.

  40. As we all know DNA stands for deoxyribonucleic acid, and it holds the genetics of a cell. It is found in the nucluos of a cell formed by nucloutides. DNA is a powerful tool because each person’s dna is different from one another, except for indentical twins. Mitochondria also holds some of the DNA, which is known as mitochondrial dna.
    The double-standard helix forms as a result of interactions between base pairs. The usual term for these interactions are stacking interactions that hold them together in a helical form. DNA bases pair up with each other, A with T and C with G to form units called base pairs. Each pair is also attached to a sugar molecule and phosphate molecule. Together, a base, sugar, and phosphate form a nuleotide. DNA can replicate, or make copies of itself.

  41. @Catalina Pacheco
    i think you wrote all the information needed about the three dimentional structres of DNA and it was staright forward, which is a good to make sure the reader doesnt get bored from what you wrote.

  42. Deoxyribonucleic acid is important to all living organisms because it contains genetic information that is used in developing and the overall function of all living organisms. Deoxyribonucleic acid is made up of a nitrogenous base, a sugar backbone group, and a phosphate group. Adenine, Guanine, Cytosine, and Thymine are the different bases found in DNA. These bases are located in the inside of the double helix. Bases Adenine and Guanine are purines. Cytosine and Thymine are pyrimidines. Adenine pairs with Thymine and Guanine pairs with cytosine because purines and pyrimidines must pair for proper bonding to occur. DNA has two different stands that run anti-parallel one going from 5’ to 3’, and its complementary strand going in the 3’ to 5’ direction.
    Will DNA structure always be the same? I think that scientist will find a way to create DNA faster because of its ability to store information and it overall importance to all living organisms. But they might find it convenient to use a single strand because it’s less complex. If they could discover how to control the single strand and get it to function as the original double strand it will be beneficial.

  43. According to Watson and Crick, it is impossible for the structure of deoxyribose nucleic acid (DNA) to have three intertwined chains as proposed by Corey and Pauling. To disapprove this structure, Watson and Crick have devised a new structure where the DNA consists of two helical chains that coil around the same fibre axis, making the structure antiparallel. Each chain has a phosphate group outside the two helices, joined by a deoxyribofuranose residue that is held by a 3’ and 5’ phosphodiester bond. Inside the helix is the sugar group and base subunits. These base units are divided into two categories, pyrimidines (adenine and guanine), and purines (thymine and cytosine). Adenine pairs with thymine and guanine pairs with cytosine respectively due to hydrogen bonding. The ratio is the same for each pairing, meaning 1 to 1 or 6 to 6, depending on the number of bases present. Watson and Crick makes the assumption that it the structure of a DNA would not exist is a ribose sugar replaces the deoxyribose because of the van der Waals forces. Van der Waals forces are the distances between atoms and their forces depend on how far or close the atom is from the other and the bonding formed between them.
    Like Watson and Crick, I also propose a similar structure of DNA that can be possible. With the vast possibilities of discovering new science, there could be another form of DNA that was unseen. In my structure, the DNA also contains two strands that wrap around the axis, but straight. The strands are also held together by hydrogen bonds with the same base pairs inside the strands. However, the inside is structured like a zipper, but each purine available still pairs with a pyrimidine. The zipper makes the inside of the DNA seem like a “zigzag” shape. I would also like to suggest that it is possible for several other helixes to join together, creating four strands in total that encircle the axis. In conclusion, any form of DNA is possible as long as it sticks to the basic units. There can be a third helix or a single helix; there are still many things to be unveiled so just keep in mind all the possibilities.

  44. In the article “Molecular Structure of Nucleic Acids” James Watson and Francis Crick propose their structure of the Deoxyribose Nucleic Acid (DNA). On a quick note i believe that this article can connect to the very first post we had done on this blog. I believe that throughout their explanation of the structure of DNA Watson and Crick put forth “good” scientific writing. Watson and Crick first begin by briefly describing the DNA structure proposed by Pauling and Corey, and support their structure by the proposition made by Fraser. After the description of the “three intertwined chains” Watson and Crick proceed to describe their double helical structure.
    Watson and Crick state that DNA has a double helix and these two strands run anti-parallel to one another, while at the same time both strands are right handed. They state that the strands run in a 3′ 5′ direction and contain ” phosphate diester groups that link the strands together”. The explanation continues to go deeper and deeper in depth in regards to the fibre axis and the phosphorus atom locations on the axis. Watson and Crick also go in depth when mentioning the bonding between the purines (adenine and guanine) and pyrimidines (thymine and cytosine). I admire the way Watson and Crick propose their idea with the proper amount of evidence, while still making it easy for readers to comprehend everything they are supporting.
    My proposition of a DNA molecule is in the formation of a circle. I’m suggesting that a DNA molecule keeps the acidic hydrogens in the strands to hold the structure together, but at the 3′ and 5′ ends of the molecule a different substance is present. This substance at one end of the DNA molecule can have its complementary atom at the opposite end, bringing the two ends of DNA toward one another. As a result, a circular form would result for the DNA strands.

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