Question

Thymine and cytosine differ from adenine and guanine in that

Answer 1

Thymine and cytosine, being pyrimidines, have a single carbon-nitrogen ring, while adenine and guanine are purines with two carbon-nitrogen rings. Base pairing in DNA consists of a purine paired with a pyrimidine, supported by hydrogen bonds. The proportion of these bases varies from species to species.

Step-by-step explanation:

Differences between Thymine and Cytosine, and Adenine and Guanine

Thymine and cytosine differ from adenine and guanine in that thymine and cytosine are pyrimidines, which have a single carbon-nitrogen ring as their primary structure, while adenine and guanine are purines, having two carbon-nitrogen rings as their primary structure.

Purines, such as adenine (A) and guanine (G), are larger structures compared to pyrimidines. Base pairing in DNA involves a purine and a pyrimidine, maintaining a consistent gap between DNA strands and ensuring a stable double helix structure. In DNA, adenine pairs with thymine, and cytosine pairs with guanine, with hydrogen bonding playing a critical role—adenine and thymine share two hydrogen bonds while cytosine and guanine share three.

Additionally, the amount of adenine, thymine, guanine, and cytosine can vary between species and can be used for species identification. However, within the same species, the variations are not significant enough for individual differentiation and do not change the base pairing principles.

Answer 2

The correct answer is: thymine and cytosine are single-ring structures called pyrimidines.

Step-by-step explanation:

Thymine, Cytosine, Adenine and Guanine are the nitrogenous bases that form the four nucleotides in DNA strands. In RNA strands, there's no thymine but there's uracil.

These bases have the function to be the fundamental units of the genetic code.

The structure of these nitrogenous bases consists of a skeleton with the shape of one ring (which grants them the name of pyrimidines) or two fused rings (these are called purines). Thymine and Cytosine are pyrimidines, while Adenine and Guanine are purines.