Multiple Choice
The size of a nucleic acid is typically expressed as the number of which of the following in it?
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7. DNA and Chromosome Structure
DNA Structure
Multiple Choice
Which of the following statements correctly describes purines and pyrimidines in DNA molecules?
A
Purines are double-ringed bases (adenine and guanine), while pyrimidines are single-ringed bases (cytosine and thymine).
B
Purines are single-ringed bases (cytosine and thymine), while pyrimidines are double-ringed bases (adenine and guanine).
C
Purines and pyrimidines are both found only in RNA, not in DNA.
D
Both purines and pyrimidines are double-ringed structures in DNA.
Verified step by step guidance1
Step 1: Understand the basic structure of nitrogenous bases in nucleic acids. There are two categories: purines and pyrimidines, which differ in their ring structures.
Step 2: Recall that purines have a double-ring structure composed of a six-membered and a five-membered nitrogen-containing ring fused together.
Step 3: Recall that pyrimidines have a single six-membered nitrogen-containing ring.
Step 4: Identify which bases belong to each category in DNA: adenine (A) and guanine (G) are purines, while cytosine (C) and thymine (T) are pyrimidines.
Step 5: Use this information to evaluate the statements and determine that the correct description is that purines are double-ringed bases (adenine and guanine), and pyrimidines are single-ringed bases (cytosine and thymine).
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