Explain the reactions taking place in mitochondrial inner membrane.

Explanation

Krebs cycle or Citric acid cycle or TCA cycle -Third stage of Aerobic Respiration :
Two molecules of acetyl CoA formed from lind reaction now enter into Krebs cycle. It is named after its discoverer, German Biochemist sir hans Adolf Krebs (1937) .The enzymes necessary for TCA cycle are found in mitochondrial matrix except succinate dehydrogenase enzyme which is found in mitochondrial inner membrane.

1. TCA cycle starts with condensation of acetyl CoA with oxaloacetate in the presence of water to yield citrate or citric acid . Therefore, it is also known as citric Acid cycle (CAC) or tri carboxylic acid (TCA) cycle .
2. It is followed by the action of different enzymes in cyclic manner.
3. During the conversion of succinyl CoA to succinate by the enzyme succinyl CoA synthetase or succinate thiokinase, a molecule of ATP synthesis from substrate without entering the electron transport chain is called substrate level phosphorylation.

4. In three (4,5,9) in this cycle `NAD^+` is reduced to `NADH^(+)+H^+` and at step 7 where FAD is reduced to `FADH_2` .
5. The summary of link reaction and Krebs cycle in mitochondria is
`{:("""Pyruvic acid "+4NAD^++FAD+4H_2O+ADP+"Pi"),(" "darr"Mitochondrial matrix"),(3CO_2+4NADH+4H^++FADH_2+H_2O+ATP):}`
6. Two molecules of pyruvic acid formed at the end of glycolysis enter into the mitochondrial matrix. Therefore, krebs cycle is repeated twice for every glucose molecule where two molecules of pyruvic acid produces six molecules of `CO_2` eight molecules of `NADH+H^+` two molecules of `FADH_2` and two molecules of ATP.