Question

Nucleic acids exhibit secondary structure. Describe through Watson- Crick Model.

Answer 1

Secondary structure

When the long chain of a polymer is arranged in the form of a helix, this helix is called a secondary structure.

Watson and Crick model of DNA

Watson and Crick proposed a double helical structure of DNA. According to their model of DNA, it has the following features:

• The two polynucleotide strands are antiparallel.
• The two DNA strands are complementary to each other:
  • Adenine [A] of one strand pairs with the Thymine [T] of the other strand with double hydrogen bonds.
  • Guanine [G] of one strand pairs with the Cytosine [C] of the other strand with triple hydrogen bonds.
• The DNA has a sugar- phosphate backbone.
• The nitrogenous bases [A, G, T, C] are present almost perpendicular to the backbone.
• The two polynucleotide strands are held together in their helical structure by hydrogen bonds between bases in opposite strands.
• The strand turns ${36}^{\circ }$ at each step of the ascent.
• One turn of the helix contains 10 base pairs.
• The length of one turn is 34$\stackrel{o}{A}$ and the distance between two base pairs is 3.4$\stackrel{o}{A}$.

Secondary structure of DNA

DNA is a polymer of nucleotides and consists of two chains of polynucleotides which form a double helix structure. Hence, DNA exhibits secondary structure.