Lecture 2 Carbohydrate PDF

# Oxidation of glucose - Glycolysis - Major pathway - Embden Meyerhof Pathway - Anaerobic glucose oxidation - Occurs inside the cytoplasm - Cytoplasm doesn’t contain O2 - **Definition:** Oxidation of glucose to give pyruvic acids in the presence of O2 (Aerobic) or to lac...

# Oxidation of glucose - Glycolysis - Major pathway - Embden Meyerhof Pathway - Anaerobic glucose oxidation - Occurs inside the cytoplasm - Cytoplasm doesn’t contain O2 - **Definition:** Oxidation of glucose to give pyruvic acids in the presence of O2 (Aerobic) or to lactic acid in the absence of O2 (Anaerobic) - **Site:** Cytoplasm of all cells. ## Steps ### 1. Phosphorylation: - Glucose + ATP -> Glucose 6-phosphate + ADP + P - the active form of glucose ### 2. Isomerization - Glucose 6-phosphate -> Fructose 6-phosphate - catalyzed by isomerase enzyme ### 3. Second phosphorylation - Fructose 6-phosphate + ATP -> Fructose 1,6 diphosphate + ADP + P - catalyzed by the enzyme phosphotructokinase ### 4. Cleavage - Fructose 1,6 diphosphate -> Dihydroxyacetone phosphate + Glyceraldehyde 3-phosphate - catalyzed by aldolase enzyme (cleavage enzyme) ### 5. Interconversion - Dihydroxyacetone phosphate -> Glyceraldehyde 3-phosphate - catalyzed by triose phosphate isomerase ### 6. Oxidation - Glyceraldehyde 3-phosphate + NAD + *P -> 1,3 Diphosphoglycerate + NADH + H - catalyzed by Glyceraldehyde 3-phosphate dehydrogenase ### 7. Substrate level phosphorylation - 1,3 Diphosphoglycerate + ADP -> 3-phosphoglycerate + ATP - catalyzed by phosphoglycerate kinase ### 8. Isomerization - 3-phosphoglycerate -> 2-phosphoglycerate - catalyzed by phosphoglycerate mutase ### 9. Dehydration - 2-phosphoglycerate -> Phosphoenolpyruvate + H2O - catalyzed by enolase ### 10. Substrate level phosphorylation - Phosphoenolpyruvate + ADP -> Pyruvate + ATP - catalyzed by pyruvate kinase ## **Glycolysis in RBCs** - RBCs do not contain mitochondria - They depend mainly on glycolysis for energy production - Glycolysis of RBCs: - Also known as Ropofert Luebering Gycle or RL cycle - Leads to the formation of Lactic acid ## **Functions of 2,3 DPG** - Dissociation of O2 from hemoglobin to pass to cells - No tissue hypoxia occurs ## **Energy Calculation** ### **In the presence of oxygen (Aerobic)** - NADH + H = 2.3 ATP - total = 8 ATP - Gain: 8 ATP - Lost: 2 ATP ### **In the absence of oxygen (Anaerobic)** - sub-level ph. 2 X 1 = 2 ATP - sub-level ph. 2 X 1 = 2 ATP - Total = 4 ATP - Gain: 4 ATP - Lost: 2 ATP # Regulation of Glycolysis - **Glycolysis is amphibolic** : - **Catabolic** for glucose conversion to pyruvate. - **Anabolic** for the production of glucose. - **Glycolysis is regulated by 3 irreversible enzymes:** - **Hexokinase:** - inhibited by high amount of glucose - Feed-back inhibition - **Phosphofructokinase (PFK):** - Pacemaker of glycolysis - inhibited by high amount of citrate - inhibited by high amount of ATP - **Pyruvate kinase:** - inhibited by high amount of ATP # Importance of Glycolysis - **Main source of energy** - **Main source of pyruvic acid (Citric acid cycle)** - **Connects between CHO & lipid metabolism by dihydroxyacetone phosphate ** - **Reversibility of glycolysis is a step of Gluconeogenesis** # Krebs Cycle - Citric acid Cycle (CAC) - After glycolysis - Pyruvic acid is produced - Pyruvate is the substrate for Krebs cycle - Pyruvate enters the Krebs cycle in the form of acetyl CoA - Before entering Krebs cycle, pyruvate is converted to acetyl CoA via oxidative decarboxylation. ## Oxidative decarboxylation - The preparatory stage for Krebs cycle - Pyruvic acid is transported from the cytoplasm to mitochondria by a specific carrier. - Oxidative decarboxylation of the ketoacid will occur to form acetyl CoA (active acetate) by pyruvate dehydrogenase complex. - Pyruvate dehydrogenase complex includes: - **Pyruvate dehydrogenase component** - **Dihydrolipoyl transacetylase** - **Dihydrolipoyl dehydrogenase** - Coenzymes involved: - **TPP** (from Vitamin B1) - **Lipoic acid** - **Coenzyme A** - **FAD** (from Vitamin B2) - **NAD** (from niacin) - **PDH complex enzyme will catalyze the formation of acetyl CoA (Active acetate) which in turn will start the Krebs Cycle** #### Coenzymes (All are derived from Vitamin B Complex) 1. **TPP** (from Vitamin B1- Thiamine) 2. **Lipoic acid** 3. **Coenzyme A** (from pantothenic acid) 4. **FAD** (from Vitamin B2 - Riboflavin) 5. **NAD** (from niacin) - **All these coenzymes are vital for the pyruvate dehydrogenase complex to function effectively.**