Introduction of Glucose Metabolism Lecture3 Fate of Pyruvate

Introduction of Glucose Metabolism Lecture-3 Fate of Pyruvate & Citric Acid Cycle

Fate of pyruvate 1 - Lactate (in cytosol) Enzyme: lactate dehyrogenase (LDH) in anaerobic glycolysis 2 - Acetyl Co. A in mitochondria Enzyme: pyruvate dehydrogenase occurs in aerobic glycolysis Acetyl Co. A is required for citric acid cycle (CAC) 3 - Oxalacetate in mitochondria Enzyme: pyruvate carboxylase Oxalacetate is required for: 1 - Citric acid cycle (condenses with acetyl Co. A): to yield energy ATP OR 2 -Gluconeogenesis (to synthesize glucose)

Fate of Pyruvate Glucose glycolysis Gluconeogenesis mitochondria OXALACETATE No Oxygen No Mitochondria OR BOTH PYRUVAT Oxygen E & Mitochondria ACETYL Co. A CITRIC ACID CYCLE LACTATE

Formation of acetyl Co. A from pyruvate • Pyruvate (end product of aerobic glycolysis) is transported into the mitochondria. • In the mitochondrial matrix, matrix pyruvate is converted to acetyl Co. A by pyruvate dehydrogenase complex (multienzyme complex) This reaction is irreversible • Pyruvate dehydrogenase complex is composed of three enzymes & five coenzymes • Coenzymes of the complex are derived from water soluble vitamins: 1 - Thiamine pyruphosphate, TPP (derived from thiamine, vitamin B 1) 2 - NAD+ (derived from niacin) 3 - FAD (derived from riboflavin) 4 - Lipoic acid 5 - Coenzyme A (derived from pantothenic acid)

Pyruvate dehydrogenase complex PYRUVATE ACETYL Co. A

Citric acid cycle or, (Krebs cycle)

Citric Acid Cycle Citric acid cycle is the final pathway where the oxidative metabolism of Carbohydrates (as glucose), proteins (amino acids) & lipids (fatty acids) to yield energy (ATP) Acetyl Co. A is the end product for oxidation of carbohydrates, lipids & proteins Acetyl Co. A condenses with oxalacetate to form citrate (first reaction of the cycle) 3 NADH are produced = 3 X 3 = 9 ATP (by oxidative phosphorylation) One FADH 2 is produced = 1 X 2 = 2 ATP (by oxidative phosphorylation) One ATP is produced (by substrate level phosphorylation) Net = 12 ATP / one acetyl Co. A

Citric Acid Cycle CYCLE - SUMMARY Acetyl Co. A 3 NADH + H 2 CO 2 1 FADH 2 1 ADP 1 ATP

Citric acid cycle or, (Krebs cycle)