The Krebs cycle takes place in the mitochondrial matrix. It is a series of enzyme-controlled reactions that completely oxidises the acetyl groups from the link reaction.
1. Acetyl coenzyme A (2C) combines with oxaloacetate (4C) to form citrate (6C). Coenzyme A is released and reused in the link reaction.
2. Citrate is decarboxylated and dehydrogenated to form a 5-carbon compound, releasing CO2 and producing reduced NAD.
3. The 5-carbon compound is decarboxylated and dehydrogenated again, forming a 4-carbon compound, CO2 and reduced NAD.
4. The 4-carbon compound is converted back to oxaloacetate in further steps. These produce one ATP by substrate-level phosphorylation, one reduced FAD and one more reduced NAD.Oxaloacetate is regenerated, so it can combine with another acetyl coenzyme A and the cycle continues.Products of one turn:
• 2 CO2
• 3 reduced NAD
• 1 reduced FAD
• 1 ATPOne glucose gives two acetyl coenzyme A, so the cycle turns twice per glucose, giving 4 CO2, 6 reduced NAD, 2 reduced FAD and 2 ATP.The Krebs cycle makes little ATP directly. Its main role is to release hydrogen, carried by reduced NAD and reduced FAD, to the electron transport chain, where most ATP is made. Its intermediates are also used to make other molecules, such as amino acids.
1. Acetyl coenzyme A (2C) combines with oxaloacetate (4C) to form citrate (6C). Coenzyme A is released and reused in the link reaction.
2. Citrate is decarboxylated and dehydrogenated to form a 5-carbon compound, releasing CO2 and producing reduced NAD.
3. The 5-carbon compound is decarboxylated and dehydrogenated again, forming a 4-carbon compound, CO2 and reduced NAD.
4. The 4-carbon compound is converted back to oxaloacetate in further steps. These produce one ATP by substrate-level phosphorylation, one reduced FAD and one more reduced NAD.Oxaloacetate is regenerated, so it can combine with another acetyl coenzyme A and the cycle continues.Products of one turn:
• 2 CO2
• 3 reduced NAD
• 1 reduced FAD
• 1 ATPOne glucose gives two acetyl coenzyme A, so the cycle turns twice per glucose, giving 4 CO2, 6 reduced NAD, 2 reduced FAD and 2 ATP.The Krebs cycle makes little ATP directly. Its main role is to release hydrogen, carried by reduced NAD and reduced FAD, to the electron transport chain, where most ATP is made. Its intermediates are also used to make other molecules, such as amino acids.