Question

If adenine makes 30% of the DNA molecule, what will be the percentage of thymine, guanine and cytosine in it?

• A. $T:20;G:25;C:25$
• B. $T:20;G:30;C:20$
• C. $T:20;G:20;C:30$
• D. $T:30;G:20;C:20$

Answer 1

The correct option is D $T:30;G:20;C:20$

According to Chargaff's rule,
[A] = [T], [G] = [C].

[A] + [G] = [C] + [T]
Purines = Pyrimidines.

Total content of DNA = 100 %

[A] + [T] + [G] + [C] = 100%

[A] = 30 % (information given in the question) and hence [T] = 30%

Hence, [G] + [C] + 30% + 30 % = 100 %

[G] + [C] = 100 % - 60 % = 40 %

[G] + [C] = 40 %

Since, [G] = [C]

40/2 = 20%

Hence, [G] = [C] = 20 %

Therefore, A - 30 %, T - 30 %, G - 20%, C - 20%