Question

If you are given the exact quantity of G and T, how will you calculate the quantity of A and C in the DNA? Why is this not possible in the RNA molecule?

Answer 1

In DNA, base pairing follows Chargaff’s rules; guanine (G) pairs with cytosine (C), so their amounts are equal (G = C). Adenine (A) pairs with thymine (T), so their amounts are also equal (A = T).

For example, if G = 50 and T = 30, then C will also be 50 (same as G) and A will be 30 (same as T). So, total bases = 50 + 50 + 30 + 30 = 160. DNA is double-stranded, and this pairing (G – C and A – T) keeps the amounts equal.

In RNA, the situation is different. RNA is usually single-stranded, so it does not strictly follow these rules.

1. In RNA, A pairs with U (uracil instead of thymine), and G pairs with C, but only in parts where the RNA folds and forms double-stranded regions.
2. Most of the RNA remains single-stranded, so many bases are unpaired. Because of this, G does not always equal C, and A does not always equal U in the whole molecule.