Question

If the base adenine constitutes 31% of an isolated DNA fragment, then what will be the expected percentage of the base cytosine in it? Explain how you arrived at the answer.

Hint:

Chargaff’s rule ensures that purines (A, G) and pyrimidines (T, C) are present in equal proportions in double-stranded DNA.

Answer 1

- DNA follows Chargaff’s rule: A = T and C = G. - If Adenine (A) constitutes 31\%, then Thymine (T) also constitutes 31\%. - The remaining percentage of the bases is: \[ 100\% - (A + T) = 100\% - 62\% = 38\%. \] - Since Cytosine (C) = Guanine (G), the remaining 38\% is equally divided: \[ C = G = \frac{38\%}{2} = 19\%. \] - Thus, the percentage of cytosine in the DNA fragment is 19\%.