Structure, properties and various forms of DNA

Structure, properties and various forms of DNA

October 24, 2021

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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MCQs on DNA structure and functions

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