If a double-stranded DNA sample contains 28% adenine (A), what percentage of the sample consists of cytosine (C)?
Answer and explanation
Correct answer: B. 22%
- Step 1: Apply Chargaff's rules for double-stranded DNA: %A = %T and %G = %C, with total sum equaling 100%.
- Step 2: If A = 28%, then T = 28%, giving A + T = 56%. The remainder is G + C = 100% - 56% = 44%. Therefore, C = 44% / 2 = 22%.
Answer
22%.
Why not the others: 28% is the thymine percentage; 44% is the sum of guanine and cytosine; 36% miscalculates total percentages.
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