Question

In the Watson and Crick model of DNA, the ‘steps’ of the ladder are composed of ______.

विकल्प

• sugars

• a purine and a pyrimidine

• two purines

• a sugar and a phosphate molecule

Answer 1

In the Watson and Crick model of DNA, the ‘steps’ of the ladder are composed of a purine and a pyrimidine.

Explanation:

In the Watson and Crick model, DNA resembles a twisted ladder where the ‘steps’ or rungs are formed by pairs of nitrogenous bases. To maintain a constant distance between the two strands, a double-ringed purine (Adenine or Guanine) always bonds with a single-ringed pyrimidine (Thymine or Cytosine). These base pairs are held together by hydrogen bonds, while the outer ‘rails’ of the ladder consist of a repeating sugar-phosphate backbone.