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: Glucose yields 36-38 ATP
• Anaerobic Glycolysis: Glucose yields 2 ATP
• Oxidative Decarboxylation of Pyruvate: 6 ATP
• Acetyl CoA Oxidation in Krebs Cycle: 12 ATP
• Substrate-Level Phosphorylation (Glycolysis): Phosphoglycerate kinase, Pyruvate kinase
• Substrate-Level Phosphorylation (Krebs Cycle): Succinate thiokinase
• Coenzymes:
  • HMP shunt: NADP
  • Glyceraldehyde-3-phosphate dehydrogenase: NAD
  • Succinate dehydrogenase: FAD
• Uronic Acid Pathway: Important for Glucuronic acid production (detoxification), UDP-glucuronic acid synthesis (vitamin C in animals)
• HMP Shunt: Produces NADPH+H and ribose-5-phosphate
• Key Enzymes (Glycolysis): Hexokinase, Glucokinase, Phosphofructokinase-1, Pyruvate Kinase
• Key Enzymes (Krebs Cycle): Citrate synthase, Isocitrate synthase, α-ketoglutarate dehydrogenase
• Key Enzymes (HMP Shunt): Glucose-6-phosphate dehydrogenase
• Key Enzymes (Glycogenesis): Glycogen synthase
• Key Enzymes (Glycogenolysis): Glycogen phosphorylase
• Key Enzymes (Gluconeogenesis): Pyruvate carboxylase, Phosphoenolpyruvate carboxykinase, Fructose-1,6-bisphosphatase, Glucose-6-phosphatase
• Glycogen Synthesis Requirements: Glycogen synthase, UDP-glucose, Branching enzyme, Glycogen primer
• Glycogen Breakdown Requirements: Glycogen phosphorylase, Inorganic phosphate, Glucan transferase, Debranching enzyme
• Glycogenolysis in Liver: Produces free glucose due to glucose-6-phosphatase
• Glycogenolysis in Muscle: Cannot produce free glucose (lacks glucose-6-phosphatase)
• Cytoplasmic Cycles: Glycolysis, Oxidative decarboxylation, HMP shunt, Uronic acid pathway, Glycogenesis, Glycogenolysis
• Mitochondrial Cycle: Krebs cycle
• Gluconeogenesis: Occurs in both cytoplasm and mitochondria
• Glycerol to Glucose: Converted to dihydroxyacetone phosphate for glucose synthesis
• Propionyl-CoA to Glucose: Converted to succinyl-CoA
• Fructose-2,6-bisphosphate: Formed from fructose-6-phosphate. Stimulates glycolysis, inhibits gluconeogenesis
• Fanconi Syndrome: Characterized by decreased reabsorption of glucose, amino acids, phosphate leading to glucosuria, aminoaciduria, phosphaturia
• Pyruvate to Acetyl-CoA: Catalyzed by pyruvate dehydrogenase complex (5 coenzymes: NAD, FAD, CoASH, TPP, Lipoic acid)
• α-Ketoglutarate to Succinyl-CoA: Catalyzed by α-ketoglutarate dehydrogenase complex (5 coenzymes)
• RBC Glycolysis: Anaerobic, ends with lactate, produces 2 ATP, independent of insulin, produces 2,3-bisphosphoglycerate
• Blood Glucose Ranges: Normal fasting blood glucose (70-110 mg/dL), 2-hour postprandial (up to 140 mg/dL), Hypoglycemia (<60 mg/dL)
• Renal Threshold for Glucose: 180 mg/dL
• Hexokinase/Glucokinase on Glucose: Glucose-6-phosphate
• Fructokinase on Fructose: Fructose-1-phosphate
• Hexokinase on Fructose: Fructose-6-phosphate
• Galactokinase on Galactose: Galactose-1-phosphate
• Hexokinase on Galactose: Galactose-6-phosphate