Which one the following is correct about `H-` bonding in nucleotides?

Options

A. `A-T, G-C`
B. `A-G, T-C`
C. `G-T, A-C`
D. `A-A, T-T`

Answer

A

Explanation

According to the Waston - Crick model, `DNA` consists of two polynucleotide strands coiled around each other in a double helix. The sugar-phosphate backbone is on the outside of the helix, and the amine bases are on the inside, so that a base on one strand points directly in toward a bases on the second strand.
The two strands run in opposite direction and are held together by hydrogen bond between pairs of bases. Ademine and thymine form two strong hydrogens bonds to each other, but not to `G` or `C` while `G` and `C` form three strong hydrogen bonds to each other, but not to `A` or `T`.