CHEM 1103 Lecture Notes - Lecture 18: Nucleic Acid Structure, Nucleic Acid Double Helix, Heterocyclic Compound
1 Mar 2019
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The cumulative zippering effect of these hydrogen bonds keeps the strands in correct complementary orientation. They are parallel to each other and ~ allow van der waal contacts between them. With just a few bases, the force is very weak. But when a dna molecule has >10,000bps, the cumulative effect is great: hydration: dna binds a significant # of water mols at its phosphoryl groups, 3" and 5" oxygen atoms in the nucleotide bases. B-dna can bind about 18-19 water mols per nucleotide. Each phosphate can bind a maximum of 6 water molecules: electrostatic interactions: dna"s external surface (the sugar phosphate backbone) possesses negatively charged phosphate groups. Block 2 between nearby phosphate groups, a potentially destabilizing force, is minimized by the shielding effects of water on divalent cations such as. Mg2+, and polycationic molecules such as the polyamines and histones: topological problems associated with strand separation (in. Decatenation = without it we cannot separate sister chromatids and.
