Question

Which ratio is constant for DNA?

(a) A + G / T + C

(b) A + T / G + C

(c) A + C / U + G

(d) A + U / G + C

This question was posed to me in a national level competition.

The above asked question is from Nucleic Acid Structure topic in chapter Nucleotides and Nucleic Acids of Biochemistry

Answer 1

Right choice is (a) A + G / T + C

Explanation: The molar concentration of purine bases A and G is equal to the molar concentration of pyrimidine bases T and C because one of each type makes up a base pair. Because of base pairing rules, A = T and G = C. The specific A – T and G – C content varies from species to species. But in any one species the ratio is constant.