Which statement correctly distinguishes pyrimidines from purines?

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Multiple Choice

Which statement correctly distinguishes pyrimidines from purines?

The main idea is that DNA and RNA bases are organized into two families based on how many rings they have: purines have two rings, while pyrimidines have one ring. This structural difference is why purines pair with pyrimidines to keep the DNA double helix width consistent. Purines include adenine and guanine; pyrimidines include cytosine and thymine in DNA, with uracil in RNA replacing thymine. So the statement that pyrimidines are single-ring bases (T, C, U) and purines are double-ring bases (A, G) correctly captures this distinction. The other options mix up which bases belong to which family (and one even mislabels thymine as a purine), so they don’t fit the actual structural difference.

The main idea is that DNA and RNA bases are organized into two families based on how many rings they have: purines have two rings, while pyrimidines have one ring. This structural difference is why purines pair with pyrimidines to keep the DNA double helix width consistent. Purines include adenine and guanine; pyrimidines include cytosine and thymine in DNA, with uracil in RNA replacing thymine. So the statement that pyrimidines are single-ring bases (T, C, U) and purines are double-ring bases (A, G) correctly captures this distinction. The other options mix up which bases belong to which family (and one even mislabels thymine as a purine), so they don’t fit the actual structural difference.

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