Biochemistry

Tricarboxylic acid cycle (Krebs cycle) During the aerobic oxidation of carbohydrates, pyruvic acid undergoes oxidative decarboxylation to form acetyl-CoA. CH, I 3 0=0 + I COOH TPP TDP HSCoA NADJA -co 2 -NADHi Pyruvate О + CO, ■> SCoA Acetyl-CoA Formed acetyl-CoA enters into various exchange reactions and is oxidized to C0 2 and H2O. The complete oxidation of acetyl-CoA occurs in the tricarboxylic acid cycle - the Krebs cycle. Up to 70% of the Pyruvic acid is oxidized to CO, and H 2 0 through the stage of formation of acetyl-CoA. During the metabolism of proteins., fats and carbohydrates, about 10 g of acetate is formed per day for each 1 kg of body weight. The Krebs cycle is the center where all metabolic pathways converge, it is the common final oxidation pathway of acetyl groups (in the form of acetyl-CoA), into which, in the process of catabolism, most of the organic molecules that play the role of “ cell fuel ” - carbohydrates, fatty acids, amino acids are transforms. It proceeds in the mitochondrial matrix and consists of eight consecutive reactions. The first reaction is catalyzed by citrate synthetase, while acetyl-CoA is condensed with oxaloacetic acid (oxaloacetate), resulting the formation of citric acid (citrate). СН Л O=C-COOH Lo * 1 ----- C^SCoA i H,C-COOH Acetyl-CoA Oxaloacetate (Oxaloacetate act'd) Citrate synthetase 11,0 HSCoA y H j > HO-C~COOH I HjC-COOH Citrate (citric acid) In the second reaction, citric acid undergoes dehydration to form cisaconitic acid, which, by adding a water molecule, is converted to isocitric acid (isocitrate). 228