Monday, November 21, 2022

Krebs cycle

The Krebs cycle is named after its discoverer, Hans Krebs. Krebs cycle is the main source of energy for cells and an important part of aerobic respiration.

It is a series of eight-step processes, where the acetyl group of acetyl-CoA is oxidized to form two molecules of CO2 and in the process, one ATP is produced. Reduced high energy compounds, NADH and FADH2 are also produced.

Krebs cycle is called citric acid cycle because the citric acid is both the first product and the final reactant of this metabolic pathway.

Before the Krebs cycle begins, a glucose molecule must be converted to acetyl-CoA. This process yields 2 acetyl-CoA molecules to be fed into the cycle.

Steps in the Krebs Cycle
Step 1: The first step is to put energy into the system. It is the condensation of acetyl CoA with 4-carbon compound oxaloacetate to form 6C citrate, coenzyme A is released. The reaction is catalyzed by citrate synthase.
Step 2: Aconitase.
Step 3: Isocitrate dehydrogenase.
Step 4: α-Ketoglutarate dehydrogenase. This step involves a highly-developed complex of 24 enzymes.
Step 5: Succinyl-CoA synthetase. This step directly produces ATP because the substrate’s link to Coenzyme A is sufficiently energetic to power the reaction. In mitochondria, the enzyme links to the Succinyl–CoA and uses the energy from releasing the coenzyme, to add a phosphate (P) to GDP to produce GTP.
Step 6: Succinate dehydrogenase.
Step 7: Fumarase.
Step 8: Malate dehydrogenase. Malate is dehydrogenated to form oxaloacetate, which combines with another molecule of acetyl CoA and starts the new cycle. Hydrogens removed, get transferred to NAD+ forming NADH.
Krebs cycle

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