Watson-Crick DNA structure

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,... 

Implicit in the functioning of the Watson-Crick DNA model is the idea that the strands of a DNA molecule must separate and new daughter strands must be synthesized in response to the sequence of bases in the mother strand. This is called semiconservative replication. Still, conservative replication, in which both strands of a daughter molecule are newly synthesized, could not be ruled out by consideration of the structure of DNA alone. 

One of the most intriguing questions is whether the Watson-Crick (WC) structures that dominate in DNA are intrinsically the most stable structures, even in the absence of the backbone and the solvent. In other words is the biological context required for these structures to be preferred It is noteworthy that theory predicts the WC structure for AT in the gas phase not to be the lowest in energy [41],... 

The structure of Watson-Crick DNA base pairs obtained by MP2 optimization127... 

DNA Structure From Mendel s Garden to Watson and Crick DNA Structure Variations on a Theme... 

List the important features of the Watson-Crick DNA double helix. Relate the base pairing of adenine "with thymine and of cytosine with guanine to the duplex structure of DNA and to the replication of the helix. Explain the molecular determinants of the specific base pairs in DNA. 

There may be no end but there was a beginning. It happened around midcentury when, within the scope of a few years, three momentous discoveries were made. The first was the construction of the a-helix and jS-sheet structures as models for stable secondary structures in proteins the second was the Watson-Crick model structure for DNA and the third was Perutz s discovery that heavy atoms, such as mercury, could be introduced into protein crystals without destroying the crystalline structure, thus making it possible to obtain information about the missing phases. At this point I indulge in some personal reminiscences, which some of my readers may choose to skip, having heard or read of them already. 

Two remarkable observations from 1948 deserve to be mentioned here. One is a forerunner of the 1953 Watson-Crick DNA double-helix structure and explains what had not yet been discovered (18, 31) ... 

The secondary structure of DNA is not only confined to double stranded Watson-Crick DNA base pairing, many... 

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. 

Early diffraction photographs of such DNA fibers taken by Rosalind Franklin and Maurice Wilkins in London and interpreted by James Watson and Francis Crick in Cambridge revealed two types of DNA structures A-DNA and B-DNA. The B-DNA form is obtained when DNA is fully hydrated as it is in vivo. A-DNA is obtained under dehydrated nonphysiological conditions. Improvements in the methods for the chemical synthesis of DNA have recently made it possible to study crystals of short DNA molecules of any selected sequence. These studies have essentially confirmed the refined fiber diffraction models for A- and B-DNA and in addition have given details of small structural variations for different DNA sequences. Furthermore, a new structural form of DNA, called Z-DNA, has been discovered. 

The breakthrough came in 1953 when James D. Watson and Francis H. C. Crick proposed a structure for DNA. The Watson-Crick proposal ranks as one of the most important in all of science and has spurred a revolution in our understanding of genetics. The structure of DNA is detailed in the next section. The boxed essay It Has Not Escaped Our Notice. .. describes how it cane about. 

In 1953, James Watson and Francis Crick made their classic proposal for the secondary structure of DNA. According to the Watson-Crick model, DNA under physiological conditions consists of two polynucleotide strands, running in opposite directions and coiled around each other in a double helix like the handrails on a spiral staircase. The two strands are complementary rather than identical and are held together by hydrogen bonds between specific pairs of... 

The DNA double heUx illustrates the contribution of multiple forces to the structure of biomolecules. While each individual DNA strand is held together by covalent bonds, the two strands of the helix are held together exclusively by noncovalent interactions. These noncovalent interactions include hydrogen bonds between nucleotide bases (Watson-Crick base pairing) and van der Waals interactions between the stacked purine and pyrimidine bases. The hehx presents the charged phosphate groups and polar ribose sugars of... 

C13-0102. hi the 1950s, Edwin Chargaff of Columbia University studied the composition of DNA from a variety of plants and animals. He found that the relative amounts of different bases changed from one species to another. However, in every species studied, the molar ratios of guanine to cytosine and of adenine to thymine were found to be very close to 1.0. Explain Chargaff s observations in terms of the Watson-Crick model of DNA structure. 

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