Question

in the process of glycolysis, formation of acetyl CoA, krebs cycle and fermentation without oxygen. How is ATP created?

Answer 1

• Glycolysis: Glycolysis is an oxidative pathway which occurs in cytoplasm of living cells. Glycolysis includes ten sequential steps which can be divided into two seperate phases: Preparatory phase is the one where glucose is phosphorylated in sixth and first carbon and then cleaved in three carbon sugar, 2ATP consumed in this phase. The other one is pay off phase where three carbon sugar is sequentially oxidized to yield ATP, NADH and pyruvate. Net gain of glycolysis without oxygen: During the pay off phase 4ATP is produced (2ATP is produced during the conversion of 1,3 bisphosphoglycerate into 3 phosphoglycerate and 2ATP is produced during the conversion of phosphoenolpyruvate into pyruvate) whereas 2ATP is consumed during the preparatory phase (1ATP is consumed during the conversion of glucose into glucose 6 phosphate and 1ATP is consumed during the conversion of fructose 6 phosphate into fructose 1,6 bisphosphate) hence net gain of ATP will be: 4ATP (ATP produced) - 2ATP (ATP consumed) = 2ATP.
• Formation of Acetyl CoA: Formation of Acetyl CoA is concerned with pyruvate decarboxylation and includes three steps: 1) Concerned with oxidative decarboxylation of pyruvate, generation of acetyl group and reaction catalysed by pyruvate dehydrogenase and released electrons are transferred to lipoic acid present in dihydrolipoyl transacetylase, thus there is reduction of lipoic acid. 2) Condensation of acetyl group with coenzyme A and produce acetyl CoA. 3) Concerned with oxidation of lipoic acid and transfer electron from lipoic acid to NAD+ via FAD.
• Kreb cycle: Kreb cycle is an oxidative pathway that completely oxidize Acetyl CoA in form of CO2 and produce NADH, FADH2 and GTP (ATP). One Kreb cycle gives off 4 pairs of hydrogen atom (8 electrons) from 1 acetyl CoA and produce 1GTP molecule during the formation of succinate. 1 molecule of acetyl CoA gives 12ATP.
• Fermentation: Fermentation is exclusively operated in absence of oxygen, there are two types of fermentation: 1) Lactic acid fermentation: In this case pyruvate is the final electron acceptor and converted in lactate and reaction is catalysed by lactate dehydrogenase. 2) Alcoholic fermentation: here final electron acceptor is acetaldehyde which is converted into ethanol. In case of fermentation NADH produced in glycolysis is consumed hence the net energy gain is 2ATP.