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Question 546
Biochemistry → General
Classification
Question
SSBAQuestion Header
A double-stranded DNA segment contains 24 adenine bases, 18 guanine bases and therefore the complementary numbers of their paired bases. How many pyrimidine bases are present in the complete double-stranded segment?
Question Stem
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Options
A
24
B
36
C
42
D
48
E
84
Explanation
In double-stranded DNA, adenine pairs with thymine and guanine pairs with cytosine. Therefore 24 adenines require 24 thymines and 18 guanines require 18 cytosines. The pyrimidines are thymine and cytosine, giving 24 + 18 = 42.
Option Validity
A) This counts thymine alone and omits cytosine.
B) This does not equal the combined number of thymine and cytosine bases required by complementary pairing.
D) This corresponds to twice the adenine count rather than total pyrimidines.
E) This is the total number of bases in both strands, not the number of pyrimidines.
Further Reading
Saxena - MRCOG-1 Basic Sciences - Biochemistry, printed p.128.