The double helical structure of DNA was proposed by James Watson and Francis Crick in 1953 (Nobel Prize, 1962). The features of Watson – crick model of DNA (B- DNA) are given below:-
1. The DNA is a right handed double helix. It is consist of two polydeoxyribonucleotides chains twisted around each other on a common axis.
2. The two strands are antiparallel i.e., one strands from 5′ to 3′ direction and other in 3′ to 5′ direction.
3. The two polypeptide chains are identical but complementary to each others.
4. The two strands are held together by hydrogen bonds formed by complementary base pairs. The A-T pairs has 2 hydrogen bonds while G-C pairs has 3 hydrogen bonds.
4. Each strand of DNA has a hydrophilic deoxyribose phosphate backbone ( 3′-5′ phosphodiester bond) on the outside of the molecule and and hydrophobic base are stacked inside.
5. The complementary base pairing in DNA helix proves Chargaff’s rule. The content of adenine equals to that of thymine and guanine equals to that of cytosine.
6. The genetic information resides on one of the two strands known as template strand or sense strand. The opposite strand is antisense strand.
7. The double helix has (wide) major grooves and narrow) minor groove along the phosphodiester backbone. Proteins interact with DNA at these grooves, without disrupting the base pairs and double helix.
