What is "catabolism"

Metabolism \Me*tab"o*lism\, n. (Physiol.)

1. The act or process, by which living tissues or cells take up and convert into their own proper substance the nutritive material brought to them by the blood, or by which they transform their cell protoplasm into simpler substances, which are fitted either for excretion or for some special purpose, as in the manufacture of the digestive enzymes. Hence, metabolism may be either constructive ( anabolism), or destructive ( catabolism).

2. (Biol.) The series of chemical changes which take place in an organism, by means of which food is manufactured and utilized and waste materials are eliminated.

Disassimilation \Dis`as*sim`i*la"tion\, n. (Physics) The decomposition of complex substances, within the organism, into simpler ones suitable only for excretion, with evolution of energy, -- a normal nutritional process the reverse of assimilation; downward metabolism; -- now more commonly called catabolism.

The breaking down of already existing chemical compounds into simpler ones, sometimes called disassimilation.
--Martin.

catabolism \catabolism\ n. the breakdown of more complex substances into simpler ones with release of energy, in living organisms; destructive or downward metabolism; -- a form of metabolism, opposed to anabolism. See also Disassimilation. [Formerly spelled katabolism.]

Syn: katabolism, dissimilation, destructive metabolism.

1876, katabolism, "destructive metabolism," from Greek katabole "a throwing down" (also "a foundation"), from kataballein "to throw down," from kata- "down" (see cata-) + ballein "to throw" (see ballistics). Barnhart says probably formed in English on the model of metabolism. Spelling Latinized from 1889.

n. (context biochemistry English) destructive metabolism, usually including the release of energy and breakdown of materials

n. breakdown of more complex substances into simpler ones with release of energy [syn: katabolism, dissimilation, destructive metabolism] [ant: anabolism]

Catabolism (from Greek κάτω kato, "downward" and βάλλειν ballein, "to throw") is the set of metabolic pathways that breaks down molecules into smaller units that are either oxidized to release energy, or used in other anabolic reactions. Catabolism breaks down large molecules (such as polysaccharides, lipids, nucleic acids and proteins) into smaller units (such as monosaccharides, fatty acids, nucleotides, and amino acids, respectively).

Cells use the monomers released from breaking down polymers to either construct new polymer molecules, or degrade the monomers further to simple waste products, releasing energy. Cellular wastes include lactic acid, acetic acid, carbon dioxide, ammonia, and urea. The creation of these wastes is usually an oxidation process involving a release of chemical free energy, some of which is lost as heat, but the rest of which is used to drive the synthesis of adenosine triphosphate (ATP). This molecule acts as a way for the cell to transfer the energy released by catabolism to the energy-requiring reactions that make up anabolism. (Catabolism is seen as destructive metabolism and anabolism as constructive metabolism). Catabolism therefore provides the chemical energy necessary for the maintenance and growth of cells. Examples of catabolic processes include glycolysis, the citric acid cycle, the breakdown of muscle protein in order to use amino acids as substrates for gluconeogenesis, the breakdown of fat in adipose tissue to fatty acids, and oxidative deamination of neurotransmitters by monoamine oxidase.

There are many signals that control catabolism. Most of the known signals are hormones and the molecules involved in metabolism itself. Endocrinologists have traditionally classified many of the hormones as anabolic or catabolic, depending on which part of metabolism they stimulate. The so-called classic catabolic hormones known since the early 20th century are cortisol, glucagon, and adrenaline (and other catecholamines). In recent decades, many more hormones with at least some catabolic effects have been discovered, including cytokines, orexin (also known as hypocretin), and melatonin.

Many of these catabolic hormones express an anti-catabolic effect in muscle tissue. One study found that the administration of epinephrine (adrenaline) had an anti-proteolytic effect, and in fact suppressed catabolism rather than promoted it. Another study found that catecholamines in general (the main ones being, epinephrine, norepinephrine and dopamine), greatly decreased the rate of muscle catabolism.