DNA Base Pairings: Why Adenine & Guanine Don't Mix

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In summary, DNA is composed of four nucleotides: Adenine, Guanine, Thymine, and Cytosine. Adenine pairs with Thymine and Guanine pairs with Cytosine due to the structure of the nucleotides. Purines, such as Adenine and Guanine, can only pair with pyrimidines, such as Thymine and Cytosine. This is because purines can form three hydrogen bonds while pyrimidines can only form two. This is illustrated by the location of the hydrogen bonds between the two DNA strands.
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Spectre5
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In DNA, the two purines are Adenine and Guanine and the two pyrimidines are Thymine and Cytosine.

NOw...in DNA...Adenine pairs with Thymine and Guanine pairs with Cytosine. A purine pairs with a pyrimidine. That explains why Adenine cannot pair with Guanine and why Thymine cannot pair with Cytosine.

However, I do not know why Adenine cannot pair with Cytosine or Guanine with Thymine...

Does anyone know why this is? If so I would greatly appreciate some insight on this. Thanks!
 
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It's due to the structure of the nucleotides. Guanine and Cytosine can form three hydrogen bonds due to their conformation, and Adenine and Thymine can only form two hydrogen bonds due to their conformation.

This site shows an illustration of the locations of the hydrogen bonds that form between the two chains, which might help you understand.
http://www.morris.umn.edu/~goochv/BiolRhyt/Lectures/dna/dna.html
Look at the illustration between points 3 and 4.
 
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  • #3
Thanks for explaining it and giving me the link, I get it now
 

1. What is DNA Base Pairing?

DNA base pairing refers to the specific pairing between the four nitrogenous bases in DNA - adenine (A), guanine (G), cytosine (C), and thymine (T). These bases form the rungs of the DNA ladder and are held together by hydrogen bonds.

2. Why do adenine and guanine not mix?

Adenine and guanine do not mix because they are both purine bases, meaning they have a double-ring structure. The nitrogenous bases in DNA can only form hydrogen bonds with their complementary base - adenine pairs with thymine (which is a single-ring pyrimidine base) and guanine pairs with cytosine (another pyrimidine base). Therefore, adenine and guanine cannot form a stable base pair with each other.

3. What is the significance of DNA base pairing?

DNA base pairing is essential for the replication and transcription of DNA. During DNA replication, the two strands of DNA separate, and each serves as a template for the synthesis of a new complementary strand. The base pairing rules ensure that the new strand has the same genetic information as the original strand. In transcription, RNA is produced from a DNA template, and base pairing allows for the correct sequence of nucleotides to be transcribed.

4. Can adenine and guanine ever pair together in DNA?

No, adenine and guanine cannot pair together in DNA. The base pairing rules are specific, and only adenine can pair with thymine and guanine with cytosine. Any other pairing would result in a mismatch, leading to potential mutations in the DNA code.

5. Are there exceptions to DNA base pairing rules?

Yes, there are exceptions to DNA base pairing rules. Some viruses, like hepatitis B, use reverse transcriptase to convert their RNA genome into DNA. This process can result in base pairing between adenine and guanine, as well as other non-traditional base pairs. However, these exceptions are rare and do not occur in the typical functioning of DNA in living organisms.

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