Krebs-cyde

Figure 8.8 The role of the Krebs cyde in the oxidation of the six common intermediates. The six short arrows indicate the positions in the cycle where the various intermediates from amino acid catabolism feed into the cycle. Eventually they are all converted to acetyl-CoA for complete oxidation by the cycle. The pathway is indicated by the broader arrows.

Krebs Cyde Supplies Electrons to the Respiratory Chain... 

The introduction of each 2-carbon unit ties up one molecule of OAA, because the acetyl group condenses with OAA to form citric add, which then travels through the cyde and becomes malate. Malate then leaves for the cytosol, and OAA is not regenerated. Consequently, continued use of acetyl groups for gluconeogenesis would lead to depletion of some of the intermediates of the Krebs cyde. This point introduces the concept that the intermediates in the Krebs cycle act in a catalytic manner in the conversion of energy fuels to CO2. 

Use of acetyl groups for gluconeogenesis results, in effect, in withdrawal of intermediates from the Krebs cyde. If continued, this withdrawal would result in cessation of the cycle. The total quantities of these intermediates present in the liver are relatively small, compared with the amount of protein in the body available for breakdown and conversion to glucose. Hence, it would make little sense to deplete the intermediates in the liver for use in gluconeogenesis. 

Thus, the reaction OA- Malate brings into action catalytic hydrogen transfer and blocks reversible decarboxylation and amino nitrogen transfer. Formation of GL from KG opens the way for amidation, while jt renders the dicarboxylate molecule inactive in CO, fixation or oxidative phosphorylation and interferes with the Krebs cyde. The conversion of GL to glutamine or of AS to aspara e stops transamination, and so on, all these interrelations being reciprocaL... 

Contrary to the majority of authors, Green, and his group maintain that their method of subfractionation yields an outer membrane fraction which possesses all of the tricarboxylic (TCA) Krebs-cyde activities of the mitochondrion. 

The citric acid cycle, also called the Krebs cycle or the tricarboxylic add (TCA) cyde, is in the mitochondria. Although oxygen is not directly required in the cyde, the pathway will not occur anaerobically because NADH and FADH will accumulate if oxygen is not available for the electron transport chain. 

Krebs cycle (citric add cyde, tricarboxylic add cyde, TCA cyde) a smes of reactions that convert the acetyl group of acetyl-CoA into two molecules of CO lactam a cyclic amide, lactone a cyclic ester. 

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