Structure and Function of DNA

Sancar, A., Structure and function of DNA photolyase and cryptochrome blue-light... 

The most obvious difference between a normal cell and a cancerous one is that control of cell division has been lost in the latter. Since cell division requires synthesis of DNA, the synthesis, structure, and function of DNA have been frequent targets for discovery of antitumor agents. One of the problems with this approach is that some perfectly normal cells in the human body also turn over rapidly, including the cells in the bone marrow that eventually lead to the blood cells and the cells that line the gut. It is not surprising that the dose-limiting toxicity of many cancer drugs is damage to the bone marrow or the gut. 

To understand the significance of these changes, it is necessary to understand the basic structure and function of DNA and its role in heredity. 

A good place to start for further information on the structure and function of DNA. 

R. Boyer, Concepts in Biochemistry (1999), Brooks/Cole (Pacific Grove, CA), pp. 30-44 280-310. Structure and function of DNA. 

G Blackburn and M Gait, Nucleic Acids m Chemistry andBiology (1991), Oxford University Press (New York) An excellent book on general aspects of nucleic acids R Boyer, Concepts m Biochemistry (1999), Brooks/Cole (Pacific Grove, CA), pp 30-44, 280-310 Structure and function of DNA... 

These brief treatments of diverse osmotic effects on DNA are adequate to show that changes in the solute composition of the nucleoplasm and cytoplasm trigger a substantial number of effects on the structure and function of DNA and chromatin. These effects, which may be lethal if not reversed, are paired with regulatory responses that lead to changes in the amounts and activities of a wide range of enzymatic, transport, and gene regulatory proteins,... 

Alter structure and function of DNA by cross-llnldng and/or fragmenting of DNA strands., ... 

Figure 23.2. Reaction mechanism of PD-DNA photolyase. A photon of blue light is absorbed by the MTHF chromophore that acts as a photoantenna. The excited energy is transferred to the flavin chromophore (FADFF). The excited flavin (FADFI ) acts as a photocatalyst and transfers an electron to a CPD in DNA. The thymines are restored to their native state and the electron is transferred back to the flavin. (Reproduced with permission from Sancar, A. Structure and function of DNA photolyase cryptochrome blue-light photoreceptors. Chem. Rev. 103, 2203-2237, 2003.)...

Statistical theories of macromolecules in solutions have recently attracted considerable attention of theorists because of remarkable and wide-ranged properti of macromolecules, of their close connection to the theories of phase transitions in lattices, and relations to ferromagnetism and adsorption problems and of the discoveries in the structures and functions of DNA and other biological macromolecules. Needless to say, a great many papers and books have been pubUshed recently, but we confine our attention to statistical theories of macromolecules in solutions. In spite of the great number of papers in this field, however, the development of rigorous statistical theories of macromolecular solutions has been rather slow, and there have been presented many different approaches some of which have probably confused readers. Therefore, in this paper we aim at a rather unified and simplified theory of macromolecular solutions and at the same time we discuss some of the feattues of various other macromolecular solution theories and elucidate the present situation. In so doing we hope to attract attention of more theoretical chemists and physicists whose participation in this field is certainly needed. 

Phosphorus is one of the most important elements on the Earth. It participates in or controls many of the biogeochemical processes occurring in the biosphere. The important role of phosphorus in the biosphere is owed to its vital role in protein synthesis. The exothermal reaction of adenosine triphosphate with photosynthesized hydrocarbons provides the subsequent biochemical reactions with energy (see structure and functions of DNA and RNA in Chapter 2, Box 5). The N P ratio in plant issues is within 8-15 (Bazilevich, 1974 Romankevich, 1982, Vitoushek and Howarth, 1991). Almost in all biogeochemical systems P was found as a deficient element limiting the productivity of ecosystems. 

FIGURE 124-9. Structure and function of DNA. Within the cellular nucleus, tightly coiled strands of DNA are packaged in units called chromosomes. Working subunits of chromosomes are called genes. During DNA replication, the double-stranded DNA helix unwinds, exposing individual nucleotides. Complementary nucleotides are retrieved and assembled by DNA polymerases to form new strands of DNA. 

The DNA molecule is a right-handed helical polymer composed of two strands. Specimens of DNA pulled into fibers fitted the observed X-ray diffraction patterns solving the structure and function of DNA. The sugar phosphates are outside. The bases are inside the helix and form complementary base pairs between the large purines (A and G) on one chain and a smaller pyrimidine base (T and C) on the other chain. Thus, base A pairs with T, whereas base G pairs with C. As a direct consequence of the base-pairing mechanism, it becomes obvious that DNA carries information by means of the linear sequence of its nucleotides. 

The gross chemical structure of DNA led to a simple conceptual understanding of genetic processes in the 1950s. We are now beginning to understand the structure and function of DNA in more detail and the Human Genome Project (Chapter 21) is attempting to formulate a complete chemical description of human DNA by early in the next century. 

Most important, each base in one chain pairs with a specific base in the other through H bonding. The essential feature of these base pairs, which is crucial to the structure and function of DNA, is that each type of base is always paired with the same partner A with T and G with C. Thus, the base sequence of one chain is the complement of the sequence of the other. For example, the sequence A—C—T on one chain is always paired with T—G—A on the other A with T, C with G, and T with A. 

A. Sancar, Structure and Function of DNA Photolyase and Cryptochrome Blue-Light Photoreceptors, Chem. Rev. 103 (2003) 2203. 

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