University:
Liberty University
Course:
BIOM 500 | Introduction to Biomedical Sciences
Academic year:

2024
Views:

439

Pages:

7
Author:

Sheha A.

Citric Acid Cycle / Kreb's Citric Acid Cycle It is also called as TCA Cycle (Tricarboxylic acid) because of the presence of 3-COOH groups in citric acid. It is a final common metabolic pathway for the oxidation of Acetyl CoA obtained from carbohydrates, lipids, and proteins to CO2, H2O and energy. Site: Mitochondria This reaction occurs in the cyclic manner and generates large amounts of ATP in the inner mitochondrial membrane. Steps Acetyl CoA (formed during pyruvate oxidation under aerobic condition and also from fatty acid oxidation) combines with oxaloacetic acid and forms citric acid and the reaction is catalysed by the condensing enzyme citrate synthetase. Citrate is converted to isocitrate by the action of aconitase enzyme. Isocitrate undergoes oxidative decarboxylation by isocitrate dehydrogenase enzyme and forms oxalosuccinate. Molecules of NADH formed enter into electron transport chain and form 3 ATP. 4. α-ketoglutarate is formed with the help of isocitrate dehydrogenase. This is a decarboxylation reaction. 5. α-ketoglutarate undergoes decarboxylation to form succinyl CoA. This is catalyzed by α-ketoglutarate dehydrogenase. In this reaction, 1 molecule of NADH is formed that enters the electron transport chain and form 3 ATP. 6. Succinyl CoA is converted into succinate by the enzyme succinate thiokinase. High energy phosphate is produced by substrate level phosphorylation. 7. Dehydrogenation of succinate is catalyzed by mitochondrial inner membrane enzyme succinate dehydrogenase. This step produces 2 ATP because of production of 1 molecule of FADH2. 8. Fumarase catalyzes the addition of water molecules to fumarate and form malate. 9. Malate is converted to oxaloacetate by malate dehydrogenase with production of 1 molecule of NADH which is equivalent to 3 ATP.