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

2024
Views:

317

Pages:

6
Author:

Sheha A.

Energetics of Krebs Cycle Step: ATP Isocitric acid → α-ketoglutaric acid 3 * 2 = 6 ATP α-ketoglutaric acid → Succinyl CoA 1 * 2 = 2 ATP Succinyl CoA → Succinic acid 1 * 2 = 2 ATP Succinic acid → Fumaric acid 2 * 2 = 4 ATP Malic acid → Oxaloacetic acid 3 * 2 = 6 ATP Total ATP: 20 ATP Inhibitors of TCA cycle: α-ketoglutarate dehydrogenase is inhibited by succinyl CoA Succinate dehydrogenase is inhibited by oxaloacetate Citrate synthase is inhibited by ATP Isocitrate dehydrogenase is inhibited by NADH It is controlled by allosteric regulation which is proportional to the energy consumption level of NADH also stimulates the TCA cycle. Citrate Synthase: inhibited by ATP, NADH, and succinyl CoA. Isocitrate dehydrogenase: inhibited by ATP and NADH, activated by ADP and calcium. α-ketoglutarate dehydrogenase: inhibited by NADH and succinyl CoA. Succinate dehydrogenase: inhibited by oxaloacetate. Malate dehydrogenase: inhibited by NADH. ADP is important for TCA cycle, if it is absent, there is no oxidation of NADH and FADH2 takes place through electron transport chain. Accumulation of NADH and FADH2 inhibit the enzymes of TCA cycle. Role of TCA cycle It is the final pathway of oxidation of carbohydrates, fats, and proteins. Oxidation of glucose to form pyruvate, and further oxidation of pyruvate to acetyl CoA. Acetyl CoA enters the TCA cycle. It is the central metabolic pathway. Intermediates of TCA cycle Oxaloacetic acid, citric acid, α-ketoglutaric acid, succinic acid, fumaric acid, malic acid. Importance of TCA cycle It is essential for the synthesis of amino acids and glucose. It is a common pathway for the oxidation of carbohydrates, fats, and proteins. It is called the amphibolic pathway because it is involved in both anabolic and catabolic processes. Primary Function of TCA Cycle: Provision of energy TCA cycle has both catabolic and anabolic roles: a) Catabolic Role: TCA cycle is the final metabolic pathway for the oxidation of carbohydrates, fats, and proteins. Oxidation of glucose to form pyruvate, and further oxidation of pyruvate to acetyl CoA. Acetyl CoA enters the TCA cycle. b) Anabolic Role: Starting from intermediates of TCA cycle, synthesis of carbohydrates, fats, and proteins (amino acids) can be done. Some intermediates of the TCA cycle are precursors for the biosynthesis of amino acids, heme, nucleotides, and other essential biomolecules.