A double-stranded DNA molecule contains a total of 120 purines and 120 pyrimidines. This DNA molecule could be composed of
A) 120 adenine and 120 uracil molecules.
B) 120 thymine and 120 adenine molecules.
C) 120 cytosine and 120 thymine molecules.
D) 120 adenine and 120 cytosine molecules.
E) 120 guanine and 120 thymine molecules.

Question

Quizplus · Accepted Answer

In a double-stranded DNA molecule, the number of purines (adenine and guanine) is equal to the number of pyrimidines (cytosine and thymine) due to base pairing rules (A pairs with T, and C pairs with G). Option B is correct because it presents a scenario where there are equal numbers of adenine and thymine, which adhere to the base pairing rules. Uracil is not found in DNA, making option A incorrect, and the other options do not correctly pair the bases according to the base pairing rules.

A Double-Stranded DNA Molecule Contains a Total of 120 Purines