Question

Why does distance between two polynucleotide chain remains const?

Answer 1

The bases in the 2 strands of DNA are paired through Hydrogen bondsand form pairs. Adenine forms 2 hydrogen bonds with thymine from opposite strand and thymine forms 2 hydrogen bonds with thymine from opposite strand
similarly guanine and cytosine are bonded with 3 h bonds as aresult of these bonds the diatance between two polynucleotide chains remain constant