METABOLISM

Metabolism is the sum of all chemical reactions in the living CELL that are used for the production of useful work, and the synthesis of cell constituents. Almost all cellular reactions are catalyzed by complex protein molecules called enzymes, which are capable of speeding reaction rates by a factor of hundreds to millions. Most structures in the living cell are complex and require periodic replacement. This process of building new molecules is called anabolism. Structures that are no longer utile are broken down into smaller molecules and either reused or excreted. This process is called catabolism.

CATABOLISM

Human growth patterns are influenced by many factors including hormones, nutrients, and even emotional environments. The most important environmental factor affecting growth is diet; which must include protein, essential vitamins and minerals, and calories. Injury and disease inhibit growth because these factors increase protein catabolism. (as a response to stress)

Inducible enzymes are involved in splitting complex substrates, or catabolism, providing energy or simple materials for the synthesis of other compounds. An inducible enzyme is produced only when the specific substrate on which it acts is present. Fro example, the enzyme beta-galactosidase, which breaks down lactose into galactose and glucose, is formed only when lactose is present. In the absence of lactose, the synthesis of this enzyme ceases.

The inducible enzyme system involves two types of genes; a regular gene (determines whether the enzyme will be produced), and one or more structural genes (specifies the amino acid sequence of the enzyme being produced). Two attachment loci on the structural genes control the movement of ribonucleic acid (RNA) polymerase molecules onto the genes.

OXIDATION AND REDUCTION

The vast majority of living organisms rely on oxygen to generate oxidative power. The actual mechanism is not a direct chemical reaction, rather a series of electron transfers through a number of intermediate compounds that readily accept and release electrons alternating between an oxidized and reduced form. This route is called the electron transport chain and is similar in all organisms. As the strongest oxidizing agent of the chain, oxygen is the final electron acceptor. Oxygen's vital role in living organisms is essentially as a substance on which to "dump" electrons. Many microorganisms are anaerobic and do not require oxygen for survival. These organisms are able to utilize sulfur and other compounds as oxidizing agents.

All organisms generate reducing power through the reversible biochemical reactions of nicotinamide-adenine dinucleotide (NAD), flavins, cytochromes, and other substances while existing in an oxidized or reduced form. By participating in the electron transport chain, the reduced form is continually regenerating from the oxidized form.