Krebs cycle

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cycle

 [si´k'l]
a succession or recurring series of events.
cardiac cycle a complete cardiac movement, or heart beat, including systole, diastole, and the intervening pause.
Cardiac cycle. From Applegate, 2000.
cell cycle the cycle of biochemical and morphological events occurring in a reproducing cell population; it consists of the S phase, occurring toward the end of interphase, in which DNA is synthesized; the G2 phase, a relatively quiescent period; the M phase, consisting of the four phases of mitosis; and the G1 phase of interphase, which lasts until the S phase of the next cycle.
citric acid cycle tricarboxylic acid cycle.
estrous cycle the recurring periods of estrus in adult females of most mammalian species and the correlated changes in the reproductive tract from one period to another.
hair cycle the successive phases of the production and then loss of hair, consisting of anagen, catagen, and telogen.
menstrual cycle see menstrual cycle.
ovarian cycle the sequence of physiologic changes in the ovary involved in ovulation; see also ovulation and reproduction.
reproductive cycle the cycle of physiologic changes in the reproductive organs, from the time of fertilization of the ovum through gestation and childbirth; see also reproduction.
sex cycle (sexual cycle)
1. the physiologic changes that recur regularly in the reproductive organs of nonpregnant female mammals.
2. the period of sexual reproduction in an organism that also reproduces asexually.
tricarboxylic acid cycle the cyclic metabolic mechanism by which the complete oxidation of the acetyl portion of acetyl-coenzyme A is effected; the process is the chief source of mammalian energy, during which carbon chains of sugars, fatty acids, and amino acids are metabolized to yield carbon dioxide, water, and high-energy phosphate bonds. Called also citric acid cycle, Krebs cycle, and TCA cycle.
 Central pathways of metabolism: How the body produces energy from the energy-containing nutrients using the tricarboxylic acid cycle. From Davis and Sherer, 1994.
urea cycle a cyclic series of reactions that produce urea; it is a major route for removal of the ammonia produced in the metabolism of amino acids in the liver and kidney.

tri·car·box·yl·ic ac·id cy·cle

together with oxidative phosphorylation, the main source of energy in the mammalian body and the end toward which carbohydrate, fat, and protein metabolism is directed; a series of reactions, beginning and ending with oxaloacetic acid, during the course of which a two-carbon fragment is completely oxidized to carbon dioxide and water with the production of 12 high-energy phosphate bonds. So called because the first four substances involved (citric acid, cis-aconitic acid, isocitric acid, and oxalosuccinic acid) are all tricarboxylic acids; from oxalosuccinate, the others are, in order, α-ketoglutarate, succinate, fumarate, l-malate, and oxaloacetate, which condenses with acetyl-CoA (from fatty acid degradation) to form citrate (citric acid) again.

Krebs cycle

(krĕbz)
n.
A series of enzymatic reactions in aerobic organisms involving oxidative metabolism of acetyl units and producing high-energy phosphate compounds such as ATP, which serve as the main source of cellular energy. Also called citric acid cycle, tricarboxylic acid cycle.

Krebs cycle

tri·car·box·yl·ic ac·id cy·cle

(TCA cycle) (trī-kahr-bok-sil'ik as'id sī'kĕl)
Together with oxidative phosphorylation, the main source of energy in the mammalian body and the end toward which carbohydrate, fat, and protein metabolism is directed; a series of reactions, beginning and ending with oxaloacetic acid, during the course of which a two-carbon fragment is completely oxidized to carbon dioxide and water with the production of 12 high-energy phosphate bonds. So called because the first four substances involved (citric acid, cis-aconitic acid, isocitric acid, and oxalosuccinic acid) are all tricarboxylic acids; from oxalosuccinate, the others are, in order, α-ketoglutarate, succinate, fumarate, l-malate, and oxaloacetate, which condenses with acetyl-CoA (from fatty acid degradation) to form citrate (citric acid) again.
Synonym(s): Krebs cycle.

Krebs cycle

A cyclical sequence of 10 biochemical reactions, brought about by mitochondrial enzymes, that involves the oxidation of a molecule of acetyl-CoA, to two molecules of carbon dioxide and water. Each turn of the cycle can result in the formation of 12 molecules of ATP per molecule of acetyl-CoA. ATP is the direct source of energy for all work performed in any cell. The Krebs cycle is one of the most important in all body biochemistry and occurs in all organisms that oxidise food totally to carbon dioxide and water. Also known as the citric acid cycle or the tricarboxylic acid cycle. (Hans Adolf Krebs, 1900–89, German-born English biochemist)
Krebs cycleclick for a larger image
Fig. 202 Krebs cycle . The major steps of the Krebs cycle.

Krebs cycle or tricarboxylic acid cycle (TCA cycle) or (formerly) citric-acid cycle

a circular series of reactions that forms part of CELL RESPIRATION in the presence of oxygen, occurring in many microorganisms as well as higher organisms. In eukaryotes the cycle occurs in the matrix of MITOCHONDRIA. The steps of the cycle were deduced by Sir Hans Krebs (1900–81), for which he received a Nobel Prize. The reactions leading up to the cycle by which ACETYLCOENZYME A is produced, together with the overall role of the cycle in the breakdown of complex molecules is described fully under AEROBIC RESPIRATION.

Each turn of the cycle releases 2 molecules of carbon dioxide, 8 hydrogen atoms that produce 11 molecules of ATP via the ELECTRON TRANSPORT SYSTEM, and 1 molecule of ATP produced by SUBSTRATE-LEVEL PHOSPHORYLATION. Two turns of the cycle are needed to complete the breakdown of one glucose molecule.

Krebs,

Sir Hans Adolph, German biochemist in England and Nobel laureate, 1900-1981.
Krebs cycle - together with oxidative phosphorylation, the main source of energy in the mammalian body and the end toward which carbohydrate, fat, and protein metabolism are directed. Synonym(s): tricarboxylic acid cycle
Krebs-Henseleit cycle - the sequence of chemical reactions, occurring primarily in the liver, that results in the production of urea. Synonym(s): urea cycle
Krebs-Ringer solution - a modification of Ringer solution.

Krebs cycle

a sequence of reactions within mitochondria, constituting the final common pathway for the oxidation of all fuel molecules (glucose, fatty acids and amino acids), in which carbon atoms enter the cycle as acetyl-CoA and emerge as carbon dioxide, and the electrons produced are transferred to the electron transport chain. Also provides intermediates for biosynthetic processes. Syn citrate cycle, citric acid cycle, tricarboxylic cycle.

cycle, Krebs 

A series of reactions in which the intermediate products of carbohydrate, fat and protein metabolism are converted to carbon dioxide and hydrogen atoms (electrons and hydrogen ions). This cycle can only operate in the presence of oxygen. Further oxidation yields carbon dioxide, water and ATP. This cycle occurs in the mitochondria that are found in the cytoplasm of cells of living organisms. It forms one of the processes in the metabolism of glucose providing energy (stored in ATP) to maintain the vital functions of the cells (e.g. mitosis). This cycle represents the principal energy pathway of the corneal endothelium. Syn. citric acid cycle; tricarboxylic acid cycle. See mitosis.
Table C9 Relationship between the minimum angle of resolution, the Snellen fraction and the equivalent spatial frequency of a sine wave
Snellen fraction
resolution (min of
arc)
(m)(ft)Spatial frequency (cpd)
0.56/320/1060
0.66/3.620/1250
0.756/4.520/1540
1.06/620/2030
1.256/7.520/2524
1.56/920/3020
2.06/1220/4015
2.56/1520/5012
4.06/2420/807.5
5.06/3020/1006
8.06/4820/1603.8
10.06/6020/2003
20.06/12020/4001.5

Krebs cycle