If a DNA molecule in an organism contains 24% cytosine, what percentage of adenine will it contain?

• A. 48%
• B. 26%
• C. 24%
• D. 52%

Answer: (B)

Verified step by step guidance

1. Recall Chargaff's rules, which state that in a double-stranded DNA molecule, the amount of cytosine (C) equals the amount of guanine (G), and the amount of adenine (A) equals the amount of thymine (T). This means \(\%C = \%G\) and \(\%A = \%T\).
2. Given that the DNA contains 24% cytosine, use Chargaff's rule to determine that guanine also makes up 24% of the DNA.
3. Calculate the combined percentage of cytosine and guanine: \(\%C + \%G = 24\% + 24\%\).
4. Since the total percentage of all four bases must equal 100%, subtract the combined percentage of C and G from 100% to find the combined percentage of adenine and thymine: \$100\% - (\%C + \%G)$.
5. Divide the combined percentage of adenine and thymine by 2 to find the percentage of adenine alone, because \(\%A = \%T\).