From citric acid cycle

NADH from citric acid cycle produce 2.5 ATP each + 15 + 15... 

Reduced flavins, reactions with oxygen 794 Reducing equivalents from citric acid cycle 515... 

Cyanide is described as a cellular toxin because it inhibits aerobic metabolism. It reversibly binds with ferric (Fe " ") iron-containing cytochrome oxidase and inhibits the last step of mitochondrial oxidative phosphorylation. This inhibition halts carbohydrate metabolism from citric acid cycle, and intracellular concentrations of adenosine triphosphate are rapidly depleted. When absorbed in high enough doses, respiratory arrest quickly ensues, which is probably caused by respiratory muscle failure. Cardiac arrest and death inevitably follow. 

Figure 21.1 Metabolic relationships among amino acids derived from citric acid cycle intermediates. 

Metabolism to lactate or ethanol non-oxidative More ATPs from Citric Acid Cycle (38 total)... 

Reoxidation of NADH from citric acid cycle -27 +67.5... 

Physiological Role of Citric Acid. Citric acid occurs ia the terminal oxidative metabolic system of virtually all organisms. This oxidative metabohc system (Fig. 2), variously called the Krebs cycle (for its discoverer, H. A. Krebs), the tricarboxyUc acid cycle, or the citric acid cycle, is a metaboHc cycle involving the conversion of carbohydrates, fats, or proteins to carbon dioxide and water. This cycle releases energy necessary for an organism s growth, movement, luminescence, chemosynthesis, and reproduction. The cycle also provides the carbon-containing materials from which cells synthesize amino acids and fats. Many yeasts, molds, and bacteria conduct the citric acid cycle, and can be selected for thek abiUty to maximize citric acid production in the process. This is the basis for the efficient commercial fermentation processes used today to produce citric acid. 

Citric acid cycle components (from rat heart mitochondria). 

Certain of the central pathways of intermediary metabolism, such as the citric acid cycle, and many metabolites of other pathways have dual purposes—they serve in both catabolism and anabolism. This dual nature is reflected in the designation of such pathways as amphibolic rather than solely catabolic or anabolic. In any event, in contrast to catabolism—which converges to the common intermediate, acetyl-CoA—the pathways of anabolism diverge from a small group of simple metabolic intermediates to yield a spectacular variety of cellular constituents. 

Oxidation of 2 molecules of glyceraldehyde-3-phosphate yields 2 NADH Pyruvate conversion to acetyl-CoA (mitochondria) 2 NADH Citric acid cycle (mitochondria) 2 molecules of GTP from 2 molecules of succinyl-CoA + 2 + 2... 

FADHg] from each citric acid cycle produce 1.5 ATP each + 3 + 3... 

ATP from the 8 N7VDH produced in the citric acid cycle (4 NADH per pyruvic acid),... 

Elucidating the stereochemistry of reaction at prochirality centers is a powerful method for studying detailed mechanisms in biochemical reactions. As just one example, the conversion of citrate to (ds)-aconitate in the citric acid cycle has been shown to occur with loss of a pro-R hydrogen, implying that the reaction takes place by an anti elimination mechanism. That is, the OH and H groups leave from opposite sides of the molecule. 

Figure 29.1 An overview of catabolic pathways for the degradation of food and the production of biochemical energy. The ultimate products of food catabolism are C02 and H2O, with the energy released in the citric acid cycle used to drive the endergonic synthesis of adenosine triphosphate (ATP) from adenosine diphosphate (ADP) plus phosphate ion, HOPO32-.

Problem 29.12 ls the pro-R or pro-5 hydrogen removed from citrate during the dehydration in step 2 of the citric acid cycle Does the elimination reaction occur with syn or anti geometry ... 

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