Question

In the light of Watson and Cricks model, describe the detailed structure of DNA.

Answer 1

• Watson and Crick proposed that the DNA is a double-stranded structure. These are twisted around each other to form a right-handed helix, called a double helix.
  
• Base-pairing occurs between a purine and pyrimidine: namely, A pairs with T and G pairs with C as adenine and thymine are complementary base pairs, and cytosine and guanine are also complementary base pairs of each other.
• Adenine and thymine are connected by two hydrogen bonds.
• Cytosine and guanine are connected by three hydrogen bonds.
• The two strands are anti-parallel in nature.
• The diameter of the DNA double helix is uniform throughout because a purine (two rings) always pairs with a pyrimidine (one ring).
• Their combined lengths are always equal.
• Also according to the chargaff's rule purines and pyrimidines exist in the ratio 1:1.
• The backbone of DNA is formed by alternating sugar and phosphate residues.