Structure, properties and various forms of DNA
Watson and Crick (1953) Double Helix Model of DNA: Salient features
- Two polynucleotide chains wound around in a right-handed (clockwise) double-helix.
- In polynucleotide chains nucleotides are joined by phosphodiester bonds. The polynucleotide chains are anti-parallel to each other: 5’ → 3’ 3’ → 5’
- Sugar-phosphate backbones of the nucleotide chains are on the outside of the double helix, and the bases are oriented towards the central axis.
- Both the polynucleotide chains are complementary to each other. The base pairing is very specific, ‘A’ always pairs with ‘T’ (2 H-bond) while ‘G’ pairs with ‘C’(3H-bond).
- Base pairs are 0.34 nm apart. The pitch of the helix is 3.4 nm, One complete helical turn has 10 bases.
- The sugar–phosphate backbones of the helix are not equally spaced along the helix axis and this creates a major groove and minor groove on the surface of the duplex
- Double helix is stabilized by two non covalent interactions: a. H- bonding b, Hydrophobic interaction.
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