Watson-Crick three-dimensional structure

One of the elegant features of the Watson-Crick three-dimensional structure for DNA was that it provided the first satisfactory explanation for the transmission of hereditary information—it explained how DNA is duplicated for the next generation. 

By now the stage was set for the discoveiy of the three-dimensional structure of DNA, the so-called secondary structure of the molecule. Some of the best minds in science were working on the problem. In 1953, James D. Watson and Francis Crick of Cambridge University announced that they had discovered the structure of DNA. 

RGURE 8-27 Base-paired helical structures in an RNA. Shown here is the possible secondary structure of the M1 RNA component of the enzyme RNase P of coli, with many hairpins RNase R which also contains a protein component (not shown), functions in the processing of transfer RNAs (see Rg. 26-23). The two brackets indicate additional complementary sequences that may be paired in the three-dimensional structure. The blue dots indicate non-Watson-Crick G=U base pairs (boxed inset). Note that G=U base pairs are allowed only when presynthesized strands of RNA fold up or anneal with each other. There are no RNA polymerases (the enzymes that synthesize RNAs on a DNA template) that insert a U opposite a template G, or vice versa, during RNA synthesis... 

Very shortly, the first question was answered in principle by Watson and Crick who proposed the three-dimensional structure of DNA in 1953. Their proposal that DNA is composed of two polynucleotide chains forming a double helix was based upon studies of x-ray diffraction patterns of DNA libers. 

Tie began working with Francis Crick in 1950 at the Cavendish laboratories. Ill 1953, Watson and Crick, using the photographs of Rosalind Franklin, which exposed crystallized molecules from the nucleus, identified the material that biologists were viewing in the nucleus as DNA. Watson and Crick created a three-dimensional structure DNA model, which provided scientists with a valuable tool in the study of heredity. In 1962 Watson-Crick were awarded the Nobel Prize for their work. 

In 1953, Watson and Crick proposed a three-dimensional structure of DNA which is a cornerstone in the history of biochemistry and molecular biology. The double helix they proposed for the secondary structure of DNA gained immediate acceptance, partly because it explained all known facts about DNA, and partly because it provided a beautiful model for DNA replication. 

In 1962, the Nobel Prize winners for Physiology and Medicine were Francis Crick, James Watson and Maurice Wilkins. They used chromatography to separate the complex mixture of amino acids making up proteins. This led to the characterization of the structure of a protein by X-ray analysis and in particular the realization that the three-dimensional structure of DNA was an inter-linked double helix. 

Base-pair hydrogen bonding of the Watson-Crick type is fundamental in all biological processes where nucleic acids are involved. These processes, which are chiefly DNA replication and protein biosynthesis [650, 651], were understood only at the molecular level when Watson and Crick discovered the three-dimensional structure of DNA [27, 527J. This structure consists of two polynucleotide chains running in opposite directions (antiparallel), and twisted into a right-handed double helix. The hydrophobic purine and pyrimidine bases are stacked in the center... 

Fig. 20.8. Three-dimensional structure of phenylalanine specific tRNA from yeast. Watson-Crick type base pairs indicated by slabs, nonstandard base-base interactions that stabilize the tertiary structure are denoted a to h. Invariant and semi-invariant nucleotides are shaded, the four double helical regions are indicated by a a-(amino add) arm, Tarm, D arm, a.c. (anticodon arm [696]...

The existence of specific base-pairing interactions was discovered in the course of studies directed at determining the three-dimensional structure of DNA. Maurice Wilkins and Rosalind Franklin obtained x-ray diffraction photographs of fibers of DNA (Figure 5.10). The characteristics of these diffraction patterns indicated that DNA was formed of two chains that wound in a regular helical structure. From these and other data, James Watson and Francis Crick inferred a structural model for DNA that accounted for the diffraction pattern and was also the source of some remarkable insights into the functional properties of nucleic acids (Figure 511). 

The diffraction pattern to be expected for a helical structure was worked out in a theoretical study by William Cochran, Francis H. C. Crick, and Vladimir Vand using the a helix as a model. This work provided the basis for the interpretation of the diffraction patterns of proteins, and also led, unexpectedly, to an understanding of nucleic acid structure. This culminated in the determination of the three-dimensional structure of DNA by James D. Watson and Frances H. C. Crick from an X-ray diffraction photograph taken by Rosalind Franklin. 

Formulating Models DNA must be copied, or replicated, before a cell can divide so that each of the two new cells that are formed by cell division has a complete set of genetic instructions. It is very important that the replicating process be accurate the new DNA molecules must be identical to the original. Watson and Crick noticed that their model for the three-dimensional structure of DNA provided a mechanism for accurate replication. 

From the beads-on-a-string linear topology, research moved to the mapping of genes in a chromosome, and later to the discovery that genes were nucleic acids. Their chemical constitution was then determined, first topologically according to the classic structural theory procedures by Todd, and finally in the three-dimensional structural pattern (3D) of the DNA double helix proposed by Watson and Crick in 1953. 

The bases in nucleic acids can interact via hydrogen bonds. The standard Watson-Crick base pairs are G-C, A T (in DNA), and A U (in RNA). Base pairing stabilizes the native three-dimensional structures of DNA and RNA. 

James Watson and Francis Crick were the first to describe the three-dimensional structure of DNA in 1953. They deduced the structure by building models based on the experimental results of others. Irwin Chargaff observed that the amount of adenine in any DNA molecule is equal to the amount of th)nnine. Similarly, he found that the amounts of cytosine and guanine are also equal. The X-ray diffraction studies of Rosalind Franklin and Maurice Wilkens revealed several repeat... 

The three-dimensional structure of DNA was deduced by Watson and Crick (1953) by analysing X-ray fibre diffraction photographs of DNA fibres recorded by Franklin and Wilkins (Franklin and Gosling 1953). This structure for DNA was arrived at by building a model which could explain the basic features of the fibre pattern. 

DNA was first isolated in 1869 from the nuclei of white blood cells. Because this material was found in the nucleus and was acidic, it was called nucleic acid. Eventually, scientists found that the nuclei of all cells contain DNA, but it wasn t until 1944 that they realized that nucleic acids are the carriers of genetic information. In 1953, James Watson and Francis Crick described the three-dimensional structure of DNA— the famed double helix. 

Most DNA molecules consist of not one but two strands (Figure 1.2). How are these strands positioned with respect to one another In 1953, James Watson and Francis Crick deduced the arrangement of these strands and proposed a three-dimensional structure for DNA molecules. 

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