Carbohydrate Metabolism Revision

Carbohydrate Metabolism Revision

• Anabolic Pathway: Glycogenesis, Gluconeogenesis
• Catabolic Pathway: Glycolysis, Oxidative decarboxylation, Krebs cycle, HMP shunt, Uronic acid pathway, Glycogenolysis
• Amphibolic Pathway: Krebs cycle
• Aerobic Glycolysis: 36-38 ATP from glucose
• Anaerobic Glycolysis: 2 ATP from glucose
• Oxidative Decarboxylation of Pyruvate: 6 ATP
• Acetyl CoA Oxidation (Krebs): 12 ATP
• Substrate-Level Phosphorylation (Glycolysis): Phosphoglycerate kinase and pyruvate kinase
• Substrate-Level Phosphorylation (Krebs Cycle): Succinate thiokinase
• Coenzymes:
  • NADP (HMP shunt)
  • NAD (Glyceraldehyde-3-phosphate dehydrogenase)
  • FAD (Succinate dehydrogenase)
• Uronic Acid Pathway: Produces glucuronic acid (important for detoxification and vitamin C synthesis in animals)
• HMP Shunt: Produces NADPH+H and ribose-5-phosphate
• Key Glycolysis Enzymes: Hexokinase, Glucokinase, Phosphofructokinase 1, Pyruvate kinase
• Key Krebs Cycle Enzymes: Citrate synthase, Isocitrate synthase, α-ketoglutarate dehydrogenase
• Key HMP Shunt Enzyme: Glucose-6-phosphate dehydrogenase
• Key Glycogenesis Enzyme: Glycogen synthase
• Key Glycogenolysis Enzyme: Glycogen phosphorylase
• Key Gluconeogenesis Enzymes: Pyruvate carboxylase, Phosphoenolpyruvate carboxykinase, Fructose 1,6-biphosphatase, Glucose-6-phosphatase
• Glycogenesis Requirements: Glycogen synthase, UDP-glucose, Branching enzyme, Glycogen primer
• Glycogenolysis Requirements: Glycogen phosphorylase, Inorganic phosphate, Glucan transferase, Debranching enzyme
• Liver Glycogenolysis: Produces free glucose due to glucose-6-phosphatase
• Muscle Glycogenolysis: Does not produce free glucose due to lack of glucose-6-phosphatase
• Cytoplasmic Cycles: Glycolysis, Oxidative decarboxylation, HMP shunt, uronic acid pathway, glycogenesis, glycogenolysis
• Mitochondrial Cycle: Krebs cycle
• Gluconeogenesis Cycle: Both cytoplasmic and mitochondrial
• Glycerol to Glucose (Gluconeogenesis): Converted to dihydroxyacetone phosphate
• Propionyl CoA to Glucose (Gluconeogenesis): Converted to succinyl CoA
• Fructose 2,6-biphosphate: Stimulates glycolysis and inhibits gluconeogenesis
• Fanconi Syndrome: Impaired renal tubular reabsorption of glucose, amino acids, and phosphate
• Pyruvate to Acetyl CoA: Requires pyruvate dehydrogenase complex (with 5 coenzymes: NAD, FAD, CoASH, TPP, and Lipoic acid)
• α-ketoglutarate to Succinyl CoA: Requires α-ketoglutarate dehydrogenase complex (with same 5 coenzymes as pyruvate dehydrogenase)
• RBC Glycolysis: Anaerobic, produces lactate, yields 2 ATP, produces 2,3-bisphosphoglycerate
• Blood Glucose Levels: Fasting (70-110 mg/dL), 2-hour PP (up to 140 mg/dL), Hypoglycemia (<60 mg/dL), Normal renal threshold (180 mg/dL)
• Glucokinase and Hexokinase Action: Convert glucose to glucose-6-phosphate
• Fructokinase Action: Converts fructose to fructose-1-phosphate
• Hexokinase Action on Fructose: Converts fructose to fructose-6-phosphate
• Galactokinase Action: Converts galactose to galactose-1-phosphate
• Hexokinase Action on Galactose: Converts galactose to galactose-6-phosphate