Showing papers on "Molecular models of DNA published in 1973"

Origins of the differences between the circular dichroism of DNA and RNA: Theoretical calculations

Abstract: Theoretical calculations of the circular dichroism of double-helical DNA and RNA by the method of Johnson and Tinoco were performed in order to investigate the origins of the optical activity spectral differences between these polynucleotides. Calculations were performed using transition moment directions arising from molecular orbital calculations as well as a transition moment directions in agreement with experimental directions. The results of these calculations indicate that the conservative circular dichroism spectrum of B-form DNA and the nonconservative spectrum of RNA (and A-form DNA) arise as a consequence of the distance between the paired bases and the helix axis. The negative nonconservative spectrum of C-form DNA was calculated and shown also to result from the distance of the paired bases from the helix axis. Several other conspicuous geometric parameters of DNA and RNA were investigated and were found to be less significant in their effects upon the spectral differences. Theoretical calculations on a four-stranded DNA model which has paired bases similarly related to the helix axis as RNA and A-form DNA was found to yield a low intensity, nonconservative circular dichroism spectrum.

Quantum Theory of DNA Summary of Results and Study Program

Abstract: Publisher Summary Deoxyribonucleic acid (DNA) plays a central role in molecular biology. The chemical and stereo structure of DNA, that is, the positions of the atomic nuclei in this macromolecule have been determined. Thus, it was possible to start the quantum-mechanical calculation of the electronic structure of DNA. These calculations compute step by step larger segments and more realistic models of DNA. The investigation of the potential surfaces acting on the protons in the hydrogen bonds of the nucleotide base pairs has given a mechanism for point mutations. The results obtained for the effect of electric field on the electronic structure of nucleotide bases and base pairs make better understanding of the mechanism of DNA duplication. The calculations help to find correlations between the electronic structure of DNA and its biological functions. The goal of the quantum mechanical investigation of DNA should be to contribute to the solution of the problem mentioned and of many other important biological problems. The chapter presents methods to investigate step by step its constituents and more and more realistic models of the real DNA molecule, respectively. Furthermore, the chapter reviews the results for the interaction between the constituent bases of the base pairs and between the stacked bases and base pairs, respectively, on the basis of different forms of the theory of van der Waals' forces.