The stability of helical polynucleotides: base contributions.

摘要: Estimates have been made of the main contributions heterocyclic bases DNA to free energies two configurations in solution, two-stranded helix and single-strand random coil. The magnitude directions dipole moments adenine, thymine, guanine cytosine base groups calculated by a semi-empirical molecular orbital treatment. Dipole—dipole, dipole—induced-dipole London force interactions among are large, make energy depend on composition sequence. stability (helix negative energy) is proportional + content. A comparison base-pair with nearest-neighbor frequency data Josse, Kaiser & Kornberg (1961) suggests that sequence natural may be influenced energy. coil difficult estimate ; it tends more from base—solvent for greater guanine—cytosine choice solvent determines these thus how melting temperature will composition. In such as water, which significant base—base exist coil, depends forces cause stacking into ordered arrays. hydrogen bond strain probably contribute little enthalpy change helix—coil transition, although they ensure specific base-pairing helix. net contribution configurational entropy changes transition also small.