Nucleic acids exhibit secondary structur | Class 11 Biology Chapter Biomolecules, Biomolecules NCERT Solutions

Nucleic acid exhibit a variety of secondary structures. The famous Watson - Crick Model says that DNA exists as a double helix. DNA is made up of two polypeptide chains arranged in double helix. The successive units are joined by phosphodiester bonds in each strand. The backbone is formed by the sugar phosphate sugar chain which is present on the outer side. Nitrogenous bases are present on the inner side and paired to each other by H- bonds. The two chains are spirally coiled around a common axis to form a regular, right handed double helix.

The helix is 20  wide, it’s one complete turn is 34  long and contains 10 base pairs. These two chains are complementary to each other. The two chains are antiparallel. One aligned in 5’ to 3’ direction and the other aligned in 3’ to 5’ direction. Adenine joined to Thymine by two hydrogen bonds and Cytosine on one chain is linked to Guanine by three hydrogen bonds. DNA is dextrorotatory.