When synthesizing a strand of double-stranded DNA, which of the following could be a plausible...
When synthesizing a strand of double-stranded DNA, which of the following could be a plausible combination of nitrogen bases?
- A. 28% Adenine, 22% cytosine, 22% guanine, 28% thymine
- B. 23% Adenine, 23% cytosine, 27% guanine, 27% uracil
- C. 48% Adenine, 52% cytosine, 52% guanine, 48% thymine
- D. 24% Adenine, 24% cytosine, 26% guanine, 26% thymine
Correct Answer: A. 28% Adenine, 22% cytosine, 22% guanine, 28% thymine
Explanation
DNA nucleotides all contain one of four possible nitrogen bases: adenine (A), thymine (T), cytosine (C), or guanine (G). In forming base pairs, an A must always pair with a T and a C must always pair with a G: [A-T], [C-G]. This means that for any DNA composition, the percent of adenine (A) must be equal to the percent of thymine (T) and, likewise, the percent of cytosine (C) must be equal to the percent of guanine (G). Looking across the answer choices, there is only one choice that satisfies this condition while also correctly summing to 100%. The choice with uracil can be eliminated immediately, since uracil only replaces thymine in RNA and is not present in DNA.