Question

How do the structure of adenine and

guanine differ from the structure of cytosine
and thymine?

Answer 1

Adenine and guanine are purines with a two-ring structure, while cytosine and thymine are pyrimidines with a single-ring structure. This difference is crucial for the consistency of DNA's double helix structure.

Step-by-step explanation:

The structure of adenine (A) and guanine (G) differs from the structure of cytosine (C) and thymine (T) in that adenine and guanine are purines, which have a two carbon-nitrogen ring structure. In contrast, cytosine and thymine are pyrimidines, possessing a single carbon-nitrogen ring structure.

The combination of a purine with a pyrimidine allows DNA to maintain a consistent structural shape, as a two-ring purine pairs with a one-ring pyrimidine, keeping the strands of the DNA helix an equal distance apart.

Answer 2

Adenine forms two hydrogen bonds with thymine in DNA while three hydrogen bonds are formed between guanine and cytosine.

Thymine and cytosine are pyrimidines because they have a single ring structure. Adenine and guanine are purines because they have a double ring structure.