Question

Adenine is 30%, what would be the percentage of guanine?

• A. 10%
• B. 20%
• C. 30%
• D. 40%

Answer 1

Answer: (B)

20%

According to Chargaff’s rule, in all cellular DNAs, regardless of the species, number of adenosine residues is equal to the number of thymidine residues which means that A=T; and the number of guanosine residues is equal to the number of cytidine residues; G = C. Hence, the sum of the purine residues equals the sum of the pyrimidine residues; i.e. A + G = T + C. Here, [A] = 30%, therefore, % of [T] is also 30%. Thus, [G]+[C] = 100 - 60 = 40%. [G] = 20% and [C] = 20%. The correct answer is B.