Watson-Crick properties

Primary and Secondary Structure. The DNA double helix was first identified by Watson and Crick in 1953 (4). Not only was the Watson-Crick model consistent with the known physical and chemical properties of DNA, but it also suggested how genetic information could be organized and rephcated, thus providing a foundation for modem molecular biology. 

DNA is a remarkably flexible molecule. Considerable rotation is possible around a number of bonds in the sugar-phosphate (phosphodeoxyribose) backbone, and thermal fluctuation can produce bending, stretching, and impairing (melting) of the strands. Many significant deviations from the Watson-Crick DNA structure are found in cellular DNA, some or all of which may play important roles in DNA metabolism. These structural variations generally do not affect the key properties of DNA defined by Watson and Crick strand complementarity,... 

The Watson-Crick structure is also referred to as B-form DNA, or B-DNA The B form is the most stable structure for a random-sequence DNA molecule under physiological conditions and is therefore the standard point of reference in any study of the properties of DNA Two structural variants that have been well characterized in crystal structures are the A and Z forms. These three DNA conformations are shown in Figure 8—19, with a summary of their properties. The A form is favored in many solutions that are relatively devoid of water. The DNA is still arranged in a right-handed double helix, but the helix is wider and the number of base pairs per helical turn is 11, rather than 10.5 as in B-DNA The... 

The hydrodynamic properties of solutions of native double-stranded DNA have thus far eluded complete quantitative interpretation, in spite of very extensive investigation. A synthesis of experimental data has recently been furnished by Doty [84 ) some of the earlier experimental results may be found in the papers of Doty, Bunce-McGiix, and Rice (86) Doty, Makmur, Eignek, and Schildkraut (55) and Kawade and Watanabe (135 ). It is easy to see that the double helices are not perfectly inflexible, for the observed intrinsic viscosities are far lower than those of rigid rods or ellipsoids with the Watson-Crick dimensions, p = Af/4600. On the other hand, the customary flexible-coil treatments also do not apply to these data. For example, if the correlation plot of against g (a) M l [) ], / is attempted, it is found that... 

Nevertheless, it could be demonstrated that the excited state properties of canonical nucleobases and base pairs are decidedly different from those of other forms [44, 45], In the case of photoexcited DNA base pairs, experimental observations indicate that the canonical, Watson-Crick isomers [7-9, 100] are considerably shorter lived by orders of magnitude than other isomers [2, 79],... 

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