Krebs cycle - the main stages and implications for biological systems

bulk of the chemical energy of carbon released into the aerobic conditions, with the participation of oxygen.The Krebs cycle is also called the citric acid cycle, or cell respiration.In deciphering the individual reactions of the process was attended by many scientists: A. Szent-Gyorgyi A. Lehninger, X. Krebs, whose name is called a cycle, SE Severin and others.

between aerobic and anaerobic breakdown of carbohydrates a close correlative connection.First of all, it is expressed in the presence of pyruvic acid, which completed the anaerobic breakdown of carbohydrates and starts cellular respiration (Krebs cycle).Both phases are catalyzed by the same enzyme.The chemical energy released by phosphorylation, is reserved in the form of ATP macroergs.The chemical reactions involved are the same coenzymes (NAD, NADP) and cations.The differences are as follows: if the anaerobic breakdown of carbohydrates mainly localized in hyaloplasm, the reaction of cellular respiration are mainly in the mitochondria.

Under certain conditions, there is antagonism between the two phases.Thus, the presence of oxygen glycolysis reaction rate decreases sharply (Pasteur effect).The products of glycolysis can inhibit aerobic metabolism of carbohydrates (Crabtree effect).

Krebs cycle is a series of chemical reactions that result in products of the breakdown of carbohydrates are oxidized to carbon dioxide and water, and chemical energy accumulated in the energy-rich compounds.During cellular respiration is produced "carrier" - oxaloacetic acid (SCHOK).Subsequently, condensation occurs with "carrier" activated acetic acid residue.There tricarboxylic acid - citric.During chemical reactions, there is a "turn" residue in acetic acid cycle.Because each molecule of pyruvic acid molecules produced eighteen adenozintrifosfatnoy acid.At the end of the loop is released "carrier", which is reacted with an activated residue new molecules of acetic acid.

Krebs cycle: reactions

If the end product of anaerobic digestion of carbohydrates is lactic acid, under the influence of lactate dehydrogenase, it is oxidized to pyruvic acid.Some molecules of pyruvic acid is the synthesis of "carrier" SCHOK influenced pyruvate carboxylase enzyme in the presence of Mg2 + ions.Some molecules of pyruvic acid is a source of "active acetate" - atsetilkoenzima A (acetyl-CoA).The reaction is carried out under the influence of pyruvate dehydrogenase.Acetyl-CoA contains a high-energy bond, which accumulates about 5-7% of energy.The bulk of the chemical energy generated by the oxidation of "active acetate".

Influenced tsitratsintetazy begins to function properly Krebs cycle, which leads to the formation of acid citrate.This acid is influenced akonitat hydratase dehydrogenated and converted into the cis-aconitic acid that after joining the water molecules becomes isocitric.Between the three tricarboxylic acids dynamic equilibrium is established.

isocitric acid is oxidized to oxalosuccinic which is decarboxylated and converted into alpha-ketoglutaric acid.The reaction is catalyzed by the enzyme isocitrate dehydrogenase.Alpha-ketoglutaric acid under the influence of an enzyme-oxo-2 (alpha-keto) -glutaratdegidrogenazy decarboxylated, resulting in the formation of succinyl-CoA comprising energy bonds.

the next step, succinyl-CoA by the enzyme succinyl-CoA synthetase GDP transmits energy bonds (guanozindifosfatnoy acid).GTP (guanozintrifosfatnaya acid) under the influence of the enzyme adenylate GTP gives energy bonds AMP (adenozinmonofosfatnoy acid).Krebs cycle: the formula - GTP + AMP - GDP + ADP.

succinic acid under the influence of the enzyme succinate dehydrogenase (LDH) is oxidized to fumarate.SDG coenzyme is flavin adenine dinucleotide.Fumarate influenced enzyme fumaratgidratazy converted into malic acid, which in turn is oxidized to form SCHOK.In the presence of the reacting system of acetyl-CoA SCHOK again included in the citric acid cycle.

So, from one molecule of glucose produces up to 38 ATP molecules (two - by anaerobic glycolysis, six - from the oxidation of two molecules of NAD ยท H + H +, which were formed during the glycolytic oksireduktsii, and 30 - by TCA).The efficiency of the TCA is 0.5.The rest of the energy is dissipated as heat.The TCA is oxidised 16-33% lactate acid, the rest of its mass is in the re-synthesis of glycogen.