biochemistry, science concerned chiefly with the chemistry of biological processes; it attempts to utilize the tools and concepts of chemistry, particularly organic and physical chemistry, for elucidation of the living system. The science has been variously referred to as physiological chemistry and as biological chemistry. Molecular biology, a term first used in 1950, is used to describe the area of research, closely related to and often overlapping biochemistry, conducted by biologists whose approach to and interest in biology are principally at the molecular level of organization. The related field of biophysics biophysics, application of various methods and principles of physical science to the study of biological problems. In physiological biophysics physical mechanisms have been used to explain such biological processes as the transmission of nerve impulses, the muscle
..... Click the link for more information. brings to biology the techniques and attitudes of the physicist. Cell biology is concerned with the organization and functioning of the individual cell and depends greatly on biochemical techniques. As the study of life forms demonstrated similar or even identical processes occurring in widely divergent species, it has taken the biochemist to unravel the underlying chemical basis for these phenomena. Biochemists study such things as the structures and physical properties of biological molecules, including the proteins, the carbohydrates, the lipids, and the nucleic acids; the mechanisms of enzyme action; the chemical regulation of metabolism; the molecular basis of genetic expression; the chemistry of vitamins; chemoluminescence; biological oxidation; and energy utilization in the cell. The study of the chemistry of the immune response offers the possibility of treatment and cure for such diseases as AIDS AIDS or acquired immunodeficiency syndrome, fatal disease caused by a rapidly mutating retrovirus that attacks the immune system and leaves the victim vulnerable to infections, malignancies, and neurological disorders.
..... Click the link for more information. and lupus lupus (l
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Bibliography

See L. Stryer, Biochemistry (3d ed. 1988); C. K. Mathews and K. E. van Holde, Biochemistry (1990); G. Zubay, Biochemistry (3d ed. 1993).

biochemistry

Field of science concerned with chemical substances and processes that occur in plants, animals, and microorganisms. It involves the quantitative determination and structural analysis of the organic compounds that make up cells (proteins, carbohydrates, and lipids) and of those that play key roles in chemical reactions vital to life (e.g., nucleic acids, vitamins, and hormones). Biochemists study cells' many complex and interrelated chemical changes. Examples include the chemical reactions by which proteins and all their precursors are synthesized, food is converted to energy (see metabolism), hereditary characteristics are transmitted (see heredity), energy is stored and released, and all biological chemical reactions are catalyzed (see catalysis, enzyme). Biochemistry straddles the biological and physical sciences and uses many techniques common in medicine and physiology as well as those of organic, analytical, and physical chemistry.

Biochemistry

The study of the substances and chemical processes which occur in living organisms. It includes the identification and quantitative determination of the substances, studies of their structure, determining how they are synthesized and degraded in organisms, and elucidating their role in the operation of the organism.

Substances studied in biochemistry include carbohydrates (including simple sugars and large polysaccharides), proteins (such as enzymes), ribonucleic acid (RNA) and deoxyribonucleic acid (DNA), lipids, minerals, vitamins, and hormones. See Carbohydrate, Deoxyribonucleic acid (dna), Enzyme, Hormone, Lipid, Protein, Ribonucleic acid (rna), Vitamin

Metabolism and energy production

Many of the chemical steps involved in the biological breakdown of sugars, lipids (fats), and amino acids are known. It is well established that living organisms capture the energy liberated from these reactions by forming a high-energy compound, adenosine triphosphate (ATP). In the absence of oxygen, some organisms and tissues derive ATP from an incomplete breakdown of glucose, degrading the sugar to an alcohol or an acid in the process. In the presence of oxygen, many organisms degrade glucose and other foodstuff to carbon dioxide and water, producing ATP in a process known as oxidative phosphorylation. See Carbohydrate metabolism, Lipid metabolism

Structure and function studies

The relationship of the structure of enzymes to their catalytic activity is becoming increasingly clear. It is now possible to visualize atoms and groups of atoms in some enzymes by x-ray crystallography. Some enzyme-catalyzed processes can now be described in terms of the spatial arrangement of the groups on the enzyme surface and how these groups influence the reacting molecules to promote the reaction. It is also possible to explain how the catalytic activity of an enzyme may be increased or decreased by changes in the shape of the enzyme molecule. An important advance has been the development of an automated procedure for joining amino acids together into a predetermined sequence. This technology will permit the synthesis of slightly altered enzymes and will improve the understanding of the relationship between the structure and the function of enzymes. In addition, this procedure permits the synthesis of medically important polypeptides (short chains of amino acids) such as some hormones and antibiotics.

Molecular genetics

A subject of intensive investigation has been the explanation of genetics in molecular terms. It is now well established that genetic information is encoded in the sequence of nucleotides of DNA and that, with the exception of some viruses which utilize RNA, DNA is the ultimate repository of genetic information. The sequence of amino acids in a protein is programmed in DNA; this information is first transferred by copying the nucleotide sequence of DNA into that of messenger RNA, from which this sequence is translated into the specific sequence of amino acids of the protein. See Genetic code, Molecular biology

The biochemical basis for a number of genetically inherited diseases, in which the cause has been traced to the production of a defective protein, has been determined. Sickle cell anemia is a striking example; it is well established that the change of a single amino acid in hemoglobin has resulted in a serious abnormality in the properties of the hemoglobin molecule. See Disease

Regulation

Increased understanding of the chemical events in biological processes has permitted the investigation of the regulation of these proceses. An important concept is the chemical feedback circuit: the product of a series of reactions can itself influence the rates of the reactions. For example, the reactions which lead to the production of ATP proceed vigorously when the supply of ATP within the cell is low, but they slow down markedly when ATP is plentiful. These observations can be explained, in part, by the fact that ATP molecules bind to some of the enzymes involved, changing the surface features of the enzymes sufficiently to decrease their effectiveness as catalysts. It is also possible to regulate these reactions by changing the amounts of the enzymes; the amount of an enzyme can be controlled by modulating the synthesis of its specific messenger RNA or by modulating the translation of the information of the RNA molecule into the enzyme molecule. Another level of regulation involves the interaction of cells and tissues in multicellular organisms. For instance, endocrine glands can sense certain tissue activities and appropriately secrete hormones which control these activities. The chemical events and substances involved in cellular and tissue “communication” have become subjects of much investigation.

Photosynthesis and nitrogen fixation

Two subjects of substantial interest are the processes of photosynthesis and nitrogen fixation. In photosynthesis, the chemical reactions whereby the gas carbon dioxide is converted into carbohydrate are understood, but the reactions whereby light energy is trapped and converted into the chemical energy necessary for the synthesis of carbohydrate are unclear. The process of nitrogen fixation involves the conversion of nitrogen gas into a chemical form which can be utilized for the synthesis of numerous biologically important substances; the chemical events of this process are not fully understood. See Nitrogen cycle, Photosynthesis