carbohydrate_biochemistry_presentation_20250829162205.pptx

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1. August 2025 Carbohydrate Digestion, Absorption & Glucose Metabolism A Comprehensive Overview of Biochemical Pathways Presentation for Undergraduate Biochemistry & Physiology Students Made with Genspark

2. Overview & Outline Presentation Structure Introduction to Carbohydrates Carbohydrate Digestion Process Carbohydrate Absorption Glucose Metabolism Overview Aerobic Breakdown of Glucose Anaerobic Breakdown of Glucose Clinical Significance Summary & Conclusion Learning Objectives After this presentation, you will be able to: Describe the process of carbohydrate digestion in the human digestive tract Explain the mechanisms of glucose, galactose, and fructose absorption in the intestine Compare aerobic and anaerobic glucose metabolism pathways Understand the clinical implications of disorders affecting these processes Continue to M I n a t d r e o w d i t u h c G t e i o n s n p a → rk

3. Introduction to Carbohydrates • Definition: Carbohydrates are organic compounds composed of carbon, hydrogen, and oxygen with the general formula (CH ₂ O)n • Classification: - Monosaccharides: Glucose, fructose, galactose - Disaccharides: Sucrose, lactose, maltose - Polysaccharides: Starch, glycogen, cellulose • Sources: Plant foods (fruits, vegetables, grains), dairy products, and stored as glycogen in animals • Biological importance: Primary energy source, structural components, and precursors for other biomolecules Key Concept: Only monosaccharides can be absorbed directly into the bloodstream, requiring digestion of larger carbohydrates before absorption Structural Features Relevant to Digestion O O H CH ₂ O H H H α - 1 linkage site Glucose ( α - D- gluc o D s i e s ) accharide (Maltose) α 1 → 4 G G Hydrolyzed by maltase Polysaccharide (Starch) G G G ... G G Hydrolyzed by amylase Made with G P e a n s g p e a r 3 k

4. Carbohydrate Digestion Process Oral Cavity Enzyme: Salivary α - amylase (ptyalin) Action: Breaks α - 1,4 glycosidic bonds in starch Products: Maltose, maltotriose, α - dextrins Stomach Action: Limited carbohydrate digestion Note: Salivary amylase inactivated by acidic pH Small Intestine Pancreatic enzymes: Pancreatic α - amylase Brush border enzymes: - - Maltase: Maltose → Glucose + Glucose Sucrase: Sucrose → Glucose + Fructose - Lactase: Lactose → Glucose + Galactose End Products: Monosaccharides (glucose, fructose, galactose) - the only forms that can be absorbed into the bloodstream Mouth Sa livary α - amylase pH ~6.8 Stomach Li mited digestion pH ~2.0 Small Intestine Brush bord er enzymes: Maltase, Sucrase, Lactase pH ~6.0- 7.4 Pancreatic α - amylase Absorption End Products: Glucose Page 4 Made with Genspark

5. Carbohydrate Absorption • Absorption Site: Small intestine epithelium (primarily jejunum) • Primary Transporters: - SGLT1 (SLC5A1): Sodium- dependent glucose cotransporter Active transport of glucose and galactose Located on apical/brush border membrane Requires Na+ gradient (powered by Na+/K+ ATPase) - GLUT5 (SLC2A5): Glucose transporter 5 Facilitates diffusion of fructose Located on apical/brush border membrane Fructose-specific transporter - GLUT2 (SLC2A2): Glucose transporter 2 Facilitates diffusion of all monosaccharides Located on basolateral membrane Enables transport to blood circulation • Post- absorption: Monosaccharides enter hepatic portal circulation to liver Key Concept: At high glucose concentrations, GLUT2 can be recruited to the apical membrane to increase absorption capacity through facilitated diffusion Intestinal Monosaccharide Absorption Intestinal Lumen Blood (Hepatic Portal Circulation) Intestinal Epithelial Cell Glucose/ Na+ Gal a S c G t o L T s e 1 Fructose GLUT5 GLUT2 All Monosaccharides Na+/K+ ATPase 3Na+ 2K+ Legend: SGLT1 GLUT2 GLUT5 Na+/K+ Made with G P e a n s g p e a r 5 k

6. Glucose Metabolism Overview • Fate of absorbed glucose: Immediate energy use (glycolysis) Storage (glycogen synthesis) Conversion to other metabolites • Key metabolic pathways: Glycolysis: Glucose → Pyruvate (cytosol) Pyruvate oxidation: Pyruvate → Acetyl- CoA Krebs cycle: Acetyl- CoA → CO ₂ + reduced cofactors Electron transport chain: NADH/FADH ₂ → ATP Fermentation: Anaerobic regeneration of NAD ⁺ • Energy yield: Complete oxidation of one glucose molecule can produce up to 30- 32 ATP molecules under aerobic conditions • Importance: Provides ATP for cellular processes, metabolic intermediates for biosynthesis, and regulatory signals Key Concept: Cellular respiration consists of both substrate-level phosphorylation (direct ATP synthesis) and oxidative phosphorylation (ATP synthesis via proton gradient) Metabolic Pathways of Glucose Glucose Glycolysis 2 ATP Pyruvate Fermentation Lactic Acid (animals) or Ethanol (yeast) Acetyl- CoA Krebs Cycl 2 e ATP Krebs Cycle NADH + FADH ₂ ETC & Oxidative 28 ATP Phosphorylation ATP (Energy) Total: 30-32 ATP per glucose Made with G P e a n s g p e a r 6 k

7. Aerobic Breakdown of Glucose • Overview: Complete oxidation of glucose to CO ₂ and H ₂ O with high ATP yield in the presence of oxygen • Three main stages: 1. Glycolysis: Cytoplasm - Glucose → 2 Pyruvate (net 2 ATP, 2 NADH) 2. Krebs Cycle: Mitochondrial matrix - Acetyl- CoA → CO ₂ (3 NADH, 1 FADH ₂ , 1 GTP per pyruvate) 3. Electron Transport Chain: Inner mitochondrial membrane - NADH/FADH ₂ → ATP via chemiosmosis ATP Yield: Total theoretical yield: 30- 32 ATP molecules per glucose Glycolysis: 2 ATP (substrate- level) Pyruvate oxidation: 2 NADH → 5 ATP Krebs cycle: 6 NADH → 15 ATP, 2 FADH ₂ → 3 ATP, 2 GTP → 2 ATP • Key Regulation Points: Phosphofructokinase-1 (glycolysis), pyruvate dehydrogenase complex, isocitrate dehydrogenase (Krebs) Aerobic Respiration Pathway Glucose (C ₆ H ₁₂ O ₆ ) Glucose GLYCOLYSIS 10 enzyme- catalyzed steps In cytoplasm 2 ATP 2 NADH 2 Pyruvate PYRUVATE OXIDATION Pyruvate dehydrogenase complex 2 NADH 2 CO ₂ 2 Acetyl- CoA KREBS CYCLE 8 enzyme- catalyzed steps per turn In mitochondrial matrix 6 NADH 2 FADH ₂ 2 GTP/ATP NADH, FADH ₂ ELECTRON TRANSPORT CHAIN Inner mitochondrial membrane 26- 28 ATP + H O Page 7 Made with Genspark

8. Anaerobic Breakdown of Glucose • Anaerobic Conditions: When oxygen is unavailable or limited (e.g., intense exercise, hypoxic environments) • Initial Process: Glycolysis continues normally, producing: - 2 ATP molecules (net gain) - 2 NADH molecules - 2 Pyruvate molecules • NAD ⁺ Regeneration: Critical for glycolysis to continue; achieved through fermentation • Key Fermentation Pathways: - Lactic Acid Fermentation: Pyruvate → Lactate (animals, some bacteria) - Alcoholic Fermentation: Pyruvate → Ethanol + CO ₂ (yeast, some bacteria) Key Concept: Anaerobic metabolism yields significantly less ATP (2 vs ~30- 32) than aerobic respiration but allows energy production when oxygen is unavailable Feature Lactic Acid Fermentation Alcoholic Fermentation Occurs in Muscle cells, some bacteria Yeast, some bacteria End products Lactate Ethanol + CO ₂ Key enzymes Lactate dehydrogenase Pyruvate decarboxylase, Alcohol dehydrogenase Net ATP yield 2 ATP per glucose 2 ATP per glucose Fermentation Pathways Glucose Glycolysis Pyruvate (2 ATP, 2 NADH) Lactate Dehydrogenase Lactic Acid (NAD ⁺ regenerated) 1. Pyruvate Decarboxylase Acetaldehyde + CO ₂ 2. Alcohol Dehydrogenase Ethanol (NAD ⁺ regenerated) Made with G P e a n s g p e a r 8 k

9. Clinical Significance • Disorders of Carbohydrate Digestion/Absorption: - Lactose Intolerance: Deficiency of lactase enzyme causing inability to digest lactose - Sucrase-Isomaltase Deficiency: Impaired digestion of sucrose and maltose - Glucose-Galactose Malabsorption: Mutation in SGLT1 gene • Metabolic Enzyme Deficiencies: - Pyruvate Kinase Deficiency: Causes hemolytic anemia, impairs ATP production - Glucose-6-Phosphate Dehydrogenase Deficiency: Affects pentose phosphate pathway - Galactosemia: Deficiency in enzymes that metabolize galactose • Metabolic Disorders: - Diabetes mellitus: Impaired glucose utilization due to insulin resistance or deficiency - Glycogen Storage Diseases: Defects in glycogen synthesis or breakdown Treatment Approaches: Dietary modifications (e.g., lactose-free diet for lactose intolerance) Enzyme replacement therapy Metabolic pathway modulation (e.g., metformin for diabetes) Disorder Affected Process Clinical Manifestations Pyruvate Kinase Deficiency Glycolysis (Final Step) Hemolytic anemia, jaundice, splenomegaly Lactose Intolerance Lactose Digestion Bloating, diarrhea, abdominal pain Type 2 Diabetes Glucose Uptake & Utilization Hyperglycemia, polyuria, polydipsia Glycogen Storage Disease Glycogen Metabolism Hypoglycemia, hepatomegaly, growth retardation Common Carbohydrate-Related Disorders Small Intestine Lumen Lactose Intolerance Mechanism With Lactase Glu c G o s a e lactose Lactase L L Intestinal Epithelium Without Lactase No Lactase GI Symptoms Made with G P e a n s g p e a r 9 k

10. Summary & Conclusion Key Takeaways Digestion cascade: Complex carbohydrates are broken down into monosaccharides through enzymatic hydrolysis (amylases, disaccharidases) Absorption mechanisms: Glucose and galactose via SGLT1 (active transport), fructose via GLUT5 (facilitated diffusion), all exit via GLUT2 Aerobic metabolism: Complete glucose oxidation yields ~30- 32 ATP via glycolysis (2 ATP), Krebs cycle (2 ATP), and oxidative phosphorylation (~26-28 ATP) Anaerobic metabolism: Net yield of only 2 ATP, with pyruvate converting to lactate or ethanol to regenerate NAD+ Clinical relevance: Digestive enzyme deficiencies, transport disorders, and metabolic diseases highlight the importance of these pathways Significance: Carbohydrate metabolism is central to cellular energetics, with multiple regulatory points that maintain homeostasis. Understanding these pathways is fundamental to biochemistry, nutrition, and medicine. Digestion Absorption Blood Transport Krebs Cycle ETC/OXPHOS ATP Energy Further Reading Textbooks: "Biochemistry" by Berg JM, Tymoczko JL, Gatto GJ, Stryer L "Harper's Illustrated Biochemistry" by Rodwell VW et al. Review Articles: Wright EM, et al. "Intestinal absorption in health and disease— sugars." Best Practice & Research Clinical Gastroenterology Mueckler M, Thorens B. "The SLC2 (GLUT) family of membrane transporters." Molecular Aspects of Medicine Integrated Pathway Overview Monosaccharides Glycolysis Page 10 Made with Genspark