Question

Why the distance between two polynucleotide chains in dna remain almost constant

Answer 1

The bases in two strands of DNA are paired through hydrogen bond (H-bonds) forming base pairs (bp). Adenine forms two hydrogen bonds with Thymine from opposite strand and vice-versa. Similarly, Guanine is bonded with Cytosine with three H-bonds. As a result of these bonds, the distance between two polynucleotide chains in DNA remains almost constant.