Question

Number of nucleotide bases of a spiral of ds-DNA molecule is

Answer 1

Introduction to structure of DNA
DNA is a double stranded helical molecule in which each strand is composed of repeating units of deoxyribonucleotides. The adjacent nucleotides are connected by phosphodiester bonds. The sugar and phosphodiester bonds form the backbone of each strand and the nitrogenous bases of each strand are projected inwards and form complementary base pairs. Adenine pairs with thymine and cytosine pairs with guanine.

Number of nucleotide bases
According to Watson and Crick model, the number of base pairs present in 1 complete turn of the DNA double helix = \(10\). As each base pair involves two nitrogenous bases of a nucleotide Thus 10 base pairs would involve \(20\) nucleotide bases or nitrogenous bases.
Final answer
(C) \(20\)