CHO Metabolism Overview

CHO Metabolism

• CHO metabolism is the study of how the body processes carbohydrates.
• It involves the fate of food molecules after digestion and absorption.
• It's a series of chemical and enzymatic reactions within the body, encompassing synthesis and breakdown of various substances.

Metabolic Pathways

• Anabolic pathways: Synthesize complex molecules from simpler ones, requiring energy.
  • Example: Protein synthesis
• Catabolic pathways: Break down complex molecules into simpler ones, releasing energy.
  • Example: Oxidative processes
• Amphibolic pathways: Act as links between anabolic and catabolic pathways.
  • Example: Citric acid cycle

Carbohydrate Metabolism

• Carbohydrates provide 50% of daily calories.
• Complete oxidation of 1 gram of carbs yields 4 kcal.
• Sources of Carbohydrates (CHO) in food:
  • Starch (50%, e.g., potatoes)
  • Sucrose and lactose (remainder)
  • Fructose and glucose (fruits, honey)

Digestion of CHO

• Polysaccharides and disaccharides must be broken down into monosaccharides for absorption.
• Enzymes involved:
  • Salivary amylase: Breaks down starch and glycogen into dextrins.
  • Pancreatic amylase: Breaks down dextrins into maltose.
  • Intestinal disaccharidases:
    • Maltase: Converts maltose into glucose.
    • Sucrase: Converts sucrose into glucose and fructose.
    • Lactase: Converts lactose into glucose and galactose.

Lactose Intolerance

• Definition: A condition where lactase enzyme is deficient, leading to lactose not being digested.
• Cause: Deficiency of lactase enzyme.
• Effects:
  • Lactose accumulates in the intestine.
  • Fermentation by intestinal bacteria.
  • Production of acids and gases.
• Symptoms: Abdominal distension, cramps, and diarrhea.
• Treatment: Lactose-free milk formula.

Metabolic Pathways of Carbohydrates

• Catabolic pathways:
  • Glycolysis
  • Hexose monophosphate shunt
  • Uronic acid pathway
  • Glycogenolysis
• Anabolic pathways:
  • Gluconeogenesis
  • Glycogenesis
• Amphibolic pathways:
  • Citric acid cycle

Glycolysis

• Definition: Oxidation of glucose to pyruvate in the presence of oxygen, or lactate in the absence.
• Major pathway of glucose oxidation.
• Site: Cytoplasm of all cells, with specific importance in:
  • Cells lacking mitochondria (e.g., red blood cells)
  • Tissues with frequent oxygen lack (e.g., skeletal muscles during exercise).
• Steps:
  • Stage 1: Energy-requiring step (glucose converted to glyceraldehyde-3-P).
  • Stage 2: Energy-producing step (glyceraldehyde-3-P converted to pyruvate or lactate).

Glycolysis in Red Blood Cells

• Mature RBCs lack mitochondria, relying solely on glycolysis.
• Lactate is the final product.
• Net energy yield: 2 ATP.
• Glucose uptake is independent of insulin.
• Critical in producing 2,3-biphosphoglycerate.

Regulation of Glycolysis

• Key enzymes (irreversible): Hexokinase/glucokinase, Phosphofructokinase-1 (PFK-1), Pyruvate kinase
• Hormonal regulation: Insulin promotes synthesis, glucagon inhibits.
• Allosteric regulation:
  • G-6-P inhibits hexokinase (not glucokinase).
  • Fructose 2,6-bisphosphate stimulates PFK-1.
  • Citrate inhibits PFK-1.
  • Fructose 2,6-bisphosphate stimulates pyruvate kinase.
• Covalent modification: Pyruvate kinase is inactivated by phosphorylation.
• Energy regulation: ADP and AMP stimulate PFK-1; ATP inhibits PFK-1 and pyruvate kinase

In Vitro Inhibition of Glycolysis

• Inhibitors:
  • Arsenate (competes with inorganic phosphate).
  • Iodoacetate (inhibits glyceraldehyde-3-phosphate dehydrogenase).
  • Fluoride (inhibits enolase).
• Clinical significance: Hemolytic anemia may result from insufficient pyruvate kinase activity in red blood cells.

Energy Production of Glycolysis

• ATP consumption (both aerobic and anaerobic): 1 ATP for converting glucose to G-6-P, 1 ATP for converting fructose-6-P to fructose 1,6 biphosphate. Net energy consumed: 2 ATP.
• ATP production (aerobic glycolysis):
  • 4 ATP by substrate-level phosphorylation (e.g., conversion of 1,3-biphosphoglycerate to 3-phosphoglycerate).
  • Other ATP from oxidative phosphorylation in mitochondria (from NADH). (either 4 or 6 ATP)
• ATP production (anaerobic glycolysis): 2 ATP by substrate-level phosphorylation.

Substrate-level phosphorylation

• Direct transfer of a phosphate group from a high-energy molecule to ADP.

This quiz dives into carbohydrate metabolism, exploring how the body processes carbohydrates after digestion and absorption. It includes key concepts like metabolic pathways, their functions, and the significance of carbohydrates as a primary energy source. Test your knowledge on anabolic, catabolic, and amphibolic pathways involved in energy production.