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Key Molecules
Enzyme
Enzymes are organic molecules that speed up chemical reactions without being used up or altered. All enzymes are proteins, but some have nonprotein portions as well. Enzymes can be used to regulate biochemical pathways. Enzyme molecules are recycled, and so are needed in very small amounts only.
1) Catalyst: Something that speeds up a chemical reaction, but is not itself used up or altered as a result.
2) Enzyme: An organic catalyst, made largely or entirely of protein.
3) Substrate: A chemical substance upon which an enzyme acts. Many enzymes are named after their substrate plus -ase. Example: the enzyme lactase digests lactose, a sugar.
4) Structure: Every enzyme has an active site that must bind to the substrate; small structural changes here have large effects and may inactivate the enzyme.
5) Isoenzymes: Most enzymes exist in several varieties, called isoenzymes or isozymes, which function alike but can be distinguished using electrophoresis, a technique that separates proteins based on their speed of migration through an electric field.
6) Function: Enzymes speed up the rate of the reaction they catalyze. The enzyme binds to the substrate, forming an enzyme-substrate complex. Reaction products are then released, and the enzyme molecule is recycled to react with another substrate molecule. Most enzymes function best at a particular pH or temperature optimum.
7) Specificity: Most enzymes match their substrates with a lock-and-key fit, and are thus highly specific to a particular substrate. Some substrates may change the shape of their enzymes to make them fit (the induced fit hypothesis).
8) Allostery: Enzyme activity often depends on a very slight freedom of controlled movement called allostery or allosteric control.
9) Inhibitors: They can inactivate enzymes by attaching to the active site, by changing the shape of the enzyme molecule, or by interfering with allostery. All enzymes can be destroyed by denaturing their proteins (as by boiling),
Vitamins  Vitamin WorldCertain enzymes need very small amounts of nonprotein components (cofactors) such as metallic ions or organic molecules called coenzymes. Vitamins are organic nutrients required in very small quantities; many vitamins are known to function as coenzymes. Cofactors: Many enzymes (and also hemoglobins and chlorophyll) cannot function properly unless a particular metallic ion (like Fe+3 or Mg+2 )is present as a cofactor.
Examples: iron in the bacterial enzyme catalase or in hemoglobin; magnesium in chlorophyll. Coenzyines: Some enzymes need organic cofactors (coenzymes). Examples: Malate dehydrogenase (in the Krebs cycle) requires the coenzyme NAD+; hemoglobin requires a ring-like heme group. Vitamins: Organic nutrients needed in our diets in very small quantities. Many vitamins function as coenzymes. Fat-soluble vitamins: Can accumulate in the body's fat reserves; chronic overdoses can thus build up to toxic levels. Vitamin A - Derived from carotene; forms rhodopsin, a light-collecting pigment in the retina. Vitamin D - Prevents rickets; regulates calcium and phosphorus metabolism. Final step in synthesis uses sunlight. Vitamin E - An anti-oxidant which protects membranes. Vitamin K - Binds calcium ions; needed for blood coagulation. Water-soluble vitamins: Circulate in body fluids. Overdoses are unlikely because excess quantities are excreted in the urine. Ascorbic acid (Vitamin C) - An anti-oxidant; promotes healthy mucous membranes and collagen; prevents scurvy. Thiamine (Vitamin B1) - Needed in carbohydrate metabolism. Riboflavin (Vitamin B2) - Part of the coenzymes FMN and FAD. Niacin (Vitamin B3) - Helps make NAD and NADP coenzymes. Pantothenic acid - Needed to make coenzyme A. Other B-group vitamins: folacin (folic acid + folate), pyridoxine(B6),cyanocobalamin (B12), biotin.
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