Question

Explain the double helix structure of DNA molecule.

Answer 1

The characteristics of the double helical structure of DNA proposed by Watson and Crick are as follows

i) The structure of DNA molecule resembles a spirally twisted ladder.

ii) It is made of two polynucleotide chains which are made of nitrogen base (Adenine, Guanine, Cytosine, and Thymine), sugar (deoxyribose sugar), and a phosphate.

iii) The two polynucleotide chains are held together by the hydrogen bonds formed between the purines and the pyrimidines (nitrogen bases)

iv) The purine A (Adenine) forms two hydrogen bonds with the pyrimidine T (Thymine) and the other purine G (Guanine) pairs with the other pyrimidine C (cytosine) via three hydrogen bonds

v) Polynucleotide chains are helically coiled and are antiparallel to each other.

v) The nitrogen bases connect the two opposite strands like the rungs of a ladder.