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Documents for "Biochemistry":

• acetylcholine a small organic molecule liberated at nerve endings as a neurotransmitter. It is particularly important in the stimulation of muscle tissue. The transmission of an impulse to the end of the nerve causes it to release neurotransmitter molecules onto the surface of the...

• ACTH see adrenocorticotropic hormone.

• actin a protein abundantly present in many cells, especially muscle cells, that significantly contributes to the cell's structure and motility. Actin can very quickly assemble into long polymer rods...

• active site see enzyme.

• adenine organic base of the purine family. Adenine combines with the sugar ribose to form adenosine, which in turn can be bonded with from one to three phosphoric acid units, yielding the three nucleotides...

• adenosine diphosphate see adenine ; adenosine triphosphate.

• adenosine monophosphate (AMP) , organic compound composed of an adenine base, the sugar ribose , and one phosphate unit. AMP is one of the possible products of the hydrolysis of adenosine triphosphate (ATP) and is therefore important in the transfer of chemical energy during anabolism. Cyclic AMP, a very close structural relative of AMP containing an additional ester linkage between the...

• adenosine triphosphate (ATP) , organic compound composed of adenine , the sugar ribose , and three phosphate groups. ATP serves as the major energy source within the cell to drive a number of biological processes such as photosynthesis, muscle contraction, and the synthesis of...

• ADH see antidiuretic hormone.

• adrenaline see epinephrine.

• adrenocorticotropic hormone polypeptide hormone secreted by the anterior pituitary gland. Its chief function is to stimulate the cortex of the adrenal gland to secrete adrenocortical steroids, chief among them cortisone. The release of adrenocorticotropic hormone (ACTH), also known as corticotropin, is stimulated by corticotropin-releasing factor (CRF), a secretion of the hypothalamus. ACTH secretion is an...

• agglutination in biochemistry: see immunity.

• alanine organic compound, one of the 20 amino acids commonly found in animal proteins. Only the l -stereoisomer participates in the biosynthesis of proteins (see stereochemistry ). Its side chain is a nonpolar, hydrophobic methyl group. The low reactivity of the amino acid permits silk, a protein which contains some 30% alanine, to have a simple, elongated structure with...

• albumin [Lat.,=white of egg], member of a class of water-soluble, heat-coagulating proteins. Albumins are widely distributed in plant and animal tissues, e.g., ovalbumin of egg, myogen of muscle, serum albumin of blood, lactalbumin of milk, legumelin of peas, and leucosin of wheat...

• aldosterone steroid secreted by the cortex of the adrenal gland. It is the most potent hormone regulating the body's electrolyte balance. Aldosterone acts directly on the kidney to decrease the rate of sodium-ion excretion (with accompanying retention of water), and to increase the rate of...

• amino acid any one of a class of simple organic compounds containing carbon, hydrogen, oxygen, nitrogen, and in certain cases sulfur. These compounds are the building blocks of proteins. They are...

• aminopterin see metabolite.

• AMP see adenosine monophosphate.

• amylase enzyme having physiological, commercial, and historical significance, also called diastase. It is found in both plants and animals. Amylase was purified (1835) from malt by Anselme Payen and Jean Persoz...

• amylopsin see amylase.

• anabolism see metabolism.

• androgen see testosterone.

• animal jelly see gelatin.

• antidiuretic hormone polypeptide hormone secreted by the posterior pituitary gland. Its principal action is to regulate the amount of water excreted by the kidneys. Antidiuretic hormone (ADH), known also as vasopressin, causes the kidneys to resorb water directly from the renal...

• antihistamine any one of a group of compounds having various chemical structures and characterized by the ability to antagonize the effects of histamine. Their principal use in medicine is in the control of allergies such as hay fever and hives. Some antihistamines are also useful as sedatives and for the prevention of motion sickness; others, such...

• antimetabolite see metabolite.

• antioxidant substance that prevents or slows the breakdown of another substance by oxygen. Synthetic and natural antioxidants are used to slow the deterioration of gasoline and rubber, and such antioxidants as...

• arginine organic compound, one of the 20 amino acids commonly found in animal proteins. Only the l -stereoisomer participates in the biosynthesis of proteins. Its basic side chain adds a positive charge and hence a greater degree of water-solubility to proteins in neutral solution. Although...

• ascorbic acid see vitamin.

• asparagine organic compound, one of the 20 amino acids commonly found in animal proteins. Only the l -stereoisomer participates in the biosynthesis of mammalian proteins. Its structure is identical to that of the amino acid aspartic acid , except that the latter compound's acidic side-chain carboxyl group has been coupled with ammonia, yielding an amide. Like glutamine , asparagine is important in the metabolism of toxic ammonia in the body. The relatively unreactive, neutral amide group in the side chain of asparagine confers no special properties upon this amino...

• aspartic acid organic compound, one of the 20 amino acids commonly found in animal proteins. Only the l -stereoisomer participates in the biosynthesis of proteins. Its acidic side chain adds a negative charge and hence a greater degree of water-solubility to proteins in neutral solution and has been...

• ATP see adenosine triphosphate.

• azathioprine see metabolite.

• beta-carotene see carotene ; antioxidant ; Vitamin A under vitamin.

• bile bitter alkaline fluid of a yellow, brown, or green color, secreted, in man, by the liver. Bile, or gall, is composed of water, bile acids and their salts, bile pigments, cholesterol, fatty acids,...

• 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...

• biotin see vitamin ; coenzyme.

• cadaverine see decay of organic matter.

• calciferol see vitamin.

• carotene long-chained, unsaturated hydrocarbon found as a pigment in many higher plants, particularly carrots, sweet potatoes, and leafy vegetables. Carotene is thought to assist in trapping light energy...

• casein well-defined group of proteins found in milk, constituting about 80% of the proteins in cow's milk, but only 40% in human milk. Casein is a remarkably efficient nutrient, supplying not only...

• catabolism subdivision of metabolism involving all degradative chemical reactions in the living cell. Large polymeric molecules such as polysaccharides, nucleic acids, and proteins are first split into their constituent monomeric...

• CDP (cytidine diphosphate): see cytosine.

• chitin main constituent of the shells of arthropods. Chitin, a polysaccharide (see carbohydrate ) analogous in chemical structure to cellulose , consists of units of a glucose derivative ( N -acetyl- d -glucosamine) joined to form a long, unbranched chain. Like cellulose, chitin contributes strength and protection to the organism. In arthropods the chitinous shell, or exoskeleton, covers the...

• cholesterol fatty lipid found in the body tissues and blood plasma of vertebrates; it is only sparingly soluble in water, but much more soluble in some organic solvents. A steroid , cholesterol can be found in large concentrations in the brain, spinal c