Deoxyribonucleic acid double-helix structure

If molecules are to be useful in the "life-business" they need to be able to copy themselves. Important here are the two nuclei acids RNA (ribonucleic acid) and DNA (deoxyribonucleic acid). DNA occurs in the nuclei of cells and is the principal component of chromosomes. It contains, in encrypted form, the instructions for the manufacture of proteins. Thus, encoded within the DNA of an organism is the order in which amino acids should be strung together to form all the necessary proteins. The clever feature of the DNA molecule is in its double helix structure, for it is this structure which allows the molecule to replicate accurately. 

DNA (deoxyribonucleic acid)—Carrier of genetic material that determines inheritance of traits. DNA is in chromosomes in every cell of the body except red blood cells and is copied when cells divide. DNA molecules are shaped like a double helix, and are composed of sequences of four bases adenosine (A), cytosine (C), guanine (G), and thymine (T). The sequence of the bases directs production of particular proteins by determining the sequence of amino acids in proteins. The double-helk structure of DNA helps it transmit genetic information. 

Nucleic acids are of great interest because they are the units of heredity, the genes, and because they control the manufacture of proteins and the functions of the cells of living organisms. Hydrogen bonds play an important part in the novel structure proposed for deoxyribonucleic acid by Watson and Crick.1,5 This structure involves a detailed eomplement riness of two intertwined polynucleotide chains, which form a double helix.117 The complementariness in structure of the two chains was attributed by Watson and Crick to the formation of hydrogen bonds between a pyrimidine residue in one chain and a purine residue in the other, for each pair of nucleotides in the chains. 

During the past half a century, fundamental scientific discoveries have been aided by the symmetry concept. They have played a role in the continuing quest for establishing the system of fundamental particles [7], It is an area where symmetry breaking has played as important a role as symmetry. The most important biological discovery since Darwin s theory of evolution was the double helical structure of the matter of heredity, DNA, by Francis Crick and James D. Watson (Figure 1-2) [8], In addition to the translational symmetry of helices (see, Chapter 8), the molecular structure of deoxyribonucleic acid as a whole has C2 rotational symmetry in accordance with the complementary nature of its two antiparallel strands [9], The discovery of the double helix was as much a chemical discovery as it was important for biology, and lately, for the biomedical sciences. 

The structure of deoxyribonucleic acid was determined in 1953 by Watson and Crick to consist of two antiparallel strands of deoxyribonucleic acid coiled around a common axis in a double helix (Fig. 6.6). The purine and pyrimidine bases are on the inside of the helix, whereas the phosphate and deoxyribose units are on the outside. The planes of the bases are perpendicular to the axis of the helix. The planes of the sugars are at approximately 70° to those of the bases. The helix diameter is 20 A adjacent bases are separated by 3.4 A along the... 

Deoxyribonucleic acid (DNA) stores the genetic information present in living cells. It allows the cell to make proteins according to a definite sequence of atoms. The DNA molecule consists of two long chains molecules twisted around each other and held together by hydrogen bonds This structure is called a double helix (Fig. 5.20). For this discovery, F. Crick, M. Wilkins and J. Watson gained the Nobel Prize for Medicine in 1962. 

One of the most important discoveries of modern science was the elucidation of the structures of DNA and RNA as the famous double helix by Watson and Crick in 1953. They realized that the basic structure of base-sugar-phosphate was ideal for a three-dimensional coil. The structure of a small part of DNA is shown on the right. Notice that the 2 (pronounced two prime ) position on the ribose ring is vacant. There is no hydroxyl group there that is why it is called deoxyribonucleic acid. The nucleotides link the two remaining OH groups on the ribose ring and these are called the 3 - and 5 -positions. This piece of DNA has three nucleotides (adenine, adenine, and thymine) and so would be called -AAT- for short. 

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