Question

The length of DNA is 510 Å. It has 20% of 6-aminopurines. Find out the total number of nucleotides and total hydrogen bonds in that DNA:

Hint:

Use base pair length (3.4 Å) to calculate total base pairs.
Double the base pairs to get total nucleotides.
Count hydrogen bonds as 2 for A-T, 3 for G-C pairs.

Answer 1

1. Length of DNA = 510 Å. One base pair length ≈ 3.4 Å.
2. Total base pairs = 510 / 3.4 ≈ 150 base pairs.
3. Total nucleotides = 150 × 2 = 300 nucleotides.
4. DNA contains 20% 6-aminopurines (A+G). In B-DNA, A pairs with T (2 H-bonds), G pairs with C (3 H-bonds).
5. Approximate total hydrogen bonds: A-T pairs = 0.2×150 = 30 pairs × 2 H = 60 H-bonds,
G-C pairs = 120 pairs × 3 H = 360 H-bonds.
6. Total H-bonds = 60 + 360 = 390. Hence correct answer is (1) 300 nucleotides, 390 Hydrogen bonds.