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Glycolysis Reaction 1 Glucose -> Glucose 6 -phosphate (G- 6 -P) The first stage of glycolysis starts from reaction of phosphorylation. Phosphorylation is catalyzed by hexokinase. It is an endothermic ATP dependent reaction and requires energy from ATP. ATP is hydrolyzed to ADP and phosphate. In such a way, glucose receives phosphate and energy. To sum up, the reaction is as follows: glucose + ATP a glucose- 6 -phosphate + ADP Reaction 2: Glucose 6 -phosphate (G- 6 -P) -> F- 6 -P (Fructose 6 -phosphate) Glucose 6 -phosphate (aldose) is changed into Fructose 6 -phosphate (ketose) (reaction of isomer ization).
It means that the position of atoms in cell is changed, whereas their quantity remains unchangeable. The reaction is possible, because the ring forms may open to the chain form, and then the aldehyde group on glucose is transformed to the kong group on fructose. The ring then closes to form the fructose- 6 -phosphate (Ophardt, c. 2303) Reaction 3: F- 6 -P (Fructose 6 -phosphate) -> FDP (Fructose 1, 6 -bisphosphate) fructose- 6 -phosphate + ATP a fructose- 1, 6 -bisphosphate + ADP The mechanism of this spontaneous reaction is very similar to reaction of Hexokinase. Fructose 6 -phosphate has an alcohol group on C- 1 that completes reaction with phosphate received from ATP to make the phosphate ester on C- 1. As well as during the Reaction 1, it is an endothermic ATP dependent reaction and requires energy from ATP, where ATP is hydrolyzed to ADP and phosphate Reaction 4: Fructose- 1, 6 -bisphosphate <-> dihydroxy acetone phosphate + glyceraldehyde- 3 -phosphate. fructose- 1, 6 -bisphosphate?
a dihydroxy acetone phosphate + glyceraldehyde- 3 -phosphate Fructose- 1, 6 -bisphosphate is split into two: an aldehyde and a ketone. It is the reverse of an aldol condensation and is catalyzed by the aldolase. The dihydroxy acetone phosphate should be changed into glyceraldehyde- 3 -phosphate to continue the reaction of glycolysis. Reaction 5: Those Phosphate Isomerase (TIM) catalyzes dihydroxy acetone phosphate (ketose) <- -> glyceraldehyde- 3 -phosphate (aldose) Glycolysis continues from glyceraldehyde- 3 -phosphate. Reaction 6: Glyceraldehyde- 3 -phosphate Dehydrogenase catalyzes glyceraldehyde- 3 -phosphate + NAD+ + Pi?
a 1, 3, bis phosphoglycerate + NADH + H+ This is the only reaction during the process of glycolysis where NAD+ is reduced to NADH. The reaction is catalyzed by glyceraldehyde- 3 -phosphate and starts as an oxidation involving the coenzyme NAD+. The aldehyde is oxidized to an acid as an intermediate through the conversion of NAD+ to NADH + H+. Then an inorganic phosphate is added in a phosphate enter synthesis (Ophardt, c. 2303) Reaction 7: Hydrolysis of Phosphate; Synthesis of ATP 1, 3 -bis phosphoglycerate + ADP? a 3 -phosphoglycerate + ATP The reaction is catalyzed by 1, 3 -bis phosphoglycerate.
The phosphate is transferred directly to an ADP to make ATP. Reaction 8: Izometrization 3 -phosphoglycerate <- -> 2 -phosphoglycerate The reaction is catalyzed by phosphoglycerate mutate. The phosphate group moves from 3 position to 2 position (izometrization): Phosphate is shifted from the hydroxyl on C 3 of 3 -phosphoglycerate to the hydroxyl on C 2. An active site histidine side-chain participates in phosphate transfer, by donating and accepting the phosphate. The process involves a 2, 3 -bisphosphate intermediate. (Diwan, n.
p. ) Reaction 9: Enolase catalyzes: 2 -phosphoglycerate? a phosphoenolpyruvate + H 2 O This is dehydration reaction which is Mg++-dependent. The reaction is catalyzed by 2 -phosphoglycerate. 2 Mg++ ions help to stabilize the enslave anion intermediate that forms when a lysine side-chain amino group extracts a proton from carbon # 2 (Diwan, n. p. ) Reaction 10: Pyruvate Kinase catalyzes phosphoenolpyruvate + ADP a pyruvate + ATP This reaction is catalyzed by Pyruvate Kinase.
Its a final reaction of glycolysis. One of phosphate groups during the process of hydrolysis creates phosphate ion and acid. The phosphate is transferred from PEP to ADP. PEP has a larger DG of phosphate hydrolysis than ATP, because removal of phosphate from PEP yields an unstable enol, that spontaneously converts to the keto form of pyruvate (p. 602). Required inorganic cations K+ and Mg++ bind to anionic residues at the active site of Pyruvate Kinase (Diwan, n. p. ) Krebs Cycle 1.
Condensation. acetyl-S-CoA takes part in a reaction of condensation with oxaloacetate to produce citrate. 2. Isometrization of Citrate. As far as one of the steps in Krebs Cycle will be a reaction of decarboxylation, the second step involves moving the hydroxyl group in molecule of citrate to form an a-keto acid later. The reaction is endergonic. 3. Generation of CO 2 by an NAD+ linked enzyme It is the first step of oxidative decarboxylation.
The reaction is catalyzed by Iso citrate dehydrogenase. 4. A Second Oxidative Decarboxylation Step This step is performed by a multi-enzyme complex, the a-Ketoglutarate Dehydrogenation Complex (Krebs Cycle n. p. ). The result of this reaction is Succinyl-CoA + NADH +CO 2 During the following steps the Succinyl-CoA is converted back into original substrate Oxaloacetate. 5. Substrate-Level Phosphorylation Succinyl CoA-Synthetase produces Succinate + GTP + CoA-SH 6. Flavin-Dependent Dehydrogenation To complete the Krebs Cycle, Succinate needs to be converted to Oxaloacetate. 7.
Hydration of a Carbon-Carbon Double Bond The reaction is catalyzed y Fumarate Hydratase to produce L-Malate 8. A Dehydrogenation Reaction that will regenerate Oxaloacetate The reaction is catalyzed by L-Malate to produce Oxaloacetate. The formation of Oxaloacetate completes the Krebs cycle. Bibliography: Florida State University Website. The Citric Acid (Krebs, TCA) Cycle [online]. 2005 [ 2005 Nov 11 ] Available from: URL: web Joyce J.
Diwan. Glycolysis and Fermentation [online]. 2005 [ 2005 Nov 11 ] Available from: URL: web Ophardt, Ch. Glycolysis Reactions [online]. 2005 [ 2005 Nov 11 ] Available from: URL: web
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