Nutrition and Metabolism Notes

Overview of Metabolism

• Metabolism: All chemical reactions in an organism.
  • Produce ATP.
  • Essential cellular functions (repair, growth, secretion, etc.).
• Catabolism: Breakdown of large molecules, releases energy (ATP).
• Anabolism: Synthesis of new molecules, requires energy.

Carbohydrate Metabolism

• Carbohydrates stored as glycogen.
• Breakdown steps: glycolysis, TCA cycle, electron transport system.
• Cellular respiration (overall reaction):
  • Glucose + oxygen \rightarrow carbon dioxide + water + energy (ATP)
  • Net gain: 36-38 ATP molecules per glucose molecule.
• Glycolysis:
  • In cytoplasm, anaerobic.
  • Glucose (6-carbon) → 2 pyruvate (3-carbon).
  • Net yield: 2 ATP.
• Preparatory Reaction:
  • Pyruvic acid converted to acetyl CoA.
• TCA Cycle (Krebs cycle, citric acid cycle):
  • In mitochondria, aerobic.
  • Cyclic.
  • Products: carbon dioxide, high-energy electrons, 2 ATP.
• Electron Transport Chain:
  • In mitochondria, aerobic.
  • Electrons transferred, energy released to make ATP.
  • Final electron acceptor: oxygen.
  • Yields 32-34 ATP.
• Gluconeogenesis:
  • Synthesis of glucose from non-carbohydrate sources (e.g., amino acids).
  • Important for brain and RBC function during low glucose.

Lipid Metabolism

• Triglycerides are the most abundant form used for energy.
• Lipid Catabolism:
  • Fatty acids removed from glycerol.
  • Glycerol converted to pyruvic acid.
  • Fatty acids generate acetyl CoA.
  • Yield more ATP/gram than carbohydrates but are slower to generate energy.
• Lipid Synthesis:
  • Excess energy stored as lipids.
• Lipid Transport:
  • Lipoproteins (chylomicrons, VLDL, LDL, HDL) transport lipids in blood.
  • LDL: "Bad cholesterol," delivers cholesterol to tissues.
  • HDL: "Good cholesterol," transports cholesterol to liver.

Protein Metabolism

• Proteins broken down into amino acids.
• Amino Acid Catabolism:
  • Deamination: Removal of amino group (-NH2).
  • Ammonia (NH3) converted to urea by the liver.
• Protein Synthesis:
  • Essential amino acids must be obtained from diet.
  • DNA dictates protein synthesis.

Metabolic Interactions

• Liver: Focal point for metabolic control, glycogen storage.
• Skeletal Muscle: Glycogen storage for muscle use.
• Adipose Tissue: Triglyceride storage.
• Neural Tissue: Requires glucose.
• Peripheral Tissues: Use glucose or fats.

Diet and Nutrition

• Nutrition: Absorption of nutrients.
• Balanced Diet: Contains necessary nutrients.
• Malnutrition: Undernutrition or overnutrition.
• Complete Proteins: Supply all essential amino acids.
• Incomplete Proteins: Deficient in essential amino acids.
• Nitrogen Balance:
  • Positive: Absorption > excretion.
  • Negative: Excretion > absorption.
• Minerals: Fluid balance, metabolic processes, enzyme cofactors.
• Vitamins:
  • Fat-soluble (A, D, E, K): Stored in fatty tissue.
  • Water-soluble (B, C): Not generally stored.

Energy Gains and Losses

• Metabolic Rate: Speed of chemical reactions.
• Basal Metabolic Rate (BMR): Minimum resting energy expenditure.
• Calorie (kilocalorie): Measure of energy (raises 1 kg of water 1°C).
• Energy Content:
  • Carbohydrate: 4 kcal/gm
  • Protein: 4 kcal/gm
  • Lipid: 9 kcal/gm
  • Alcohol: 7 kcal/gm (empty calories).

Thermoregulation

• Heat Transfer:
  • Radiation, conduction, convection, evaporation.
  • Insensible water loss, sensible perspiration.
• Heat Gain/Loss:
  • Increase loss: Peripheral vasodilation, perspiration, increased respiration.
  • Promote gain: Vasoconstriction, shivering/non-shivering thermogenesis.
• Variations:
  • Acclimatization, infants (undeveloped mechanisms), adults (adipose insulation).
• Fever:
  • Pyrexia: Elevated body temperature (>37.2° C).