Nutrition, Metabolism, and Temperature Regulation Overview

Chapter 25: Nutrition, Metabolism and Temperature Regulation

25.2 Metabolism
  • Metabolism: Refers to all the chemical changes that occur in the cell or body.
  • Catabolism: An energy-releasing process where large molecules are broken down into smaller ones.
  • Anabolism: An energy-requiring process where small molecules are joined to form larger molecules.
ATP and Energy Transfer
  • ATP Production:
    • Derived from catabolic reactions; energy released from food fuels ATP production.
    • Breakdown of ATP involves converting ATP to ADP (adenosine diphosphate) and phosphate, which releases energy used in anabolic processes.
Pathways of ATP Production
  • Substrates:
    • Lipid: Fatty acids and glycerol.
    • Carbohydrate: Monosaccharides e.g., glucose.
    • Protein: Amino acids.
    • Processes:
    • Glycolysis → Pyruvic acid → Acetyl-CoA → Citric acid cycle → Electron transport chain.
    • Results in the production of CO₂, H₂O, and ATP.
25.3 Carbohydrate Metabolism
  • Monosaccharides: Breakdown products of carbohydrate digestion. Glucose is the most important.
  • Glycogenesis: The conversion of excess glucose into glycogen for storage in the liver and skeletal muscles.
Glycolysis
  • Process:
    • Glucose is broken down into two pyruvate molecules.
    • Input: 2 ATP used to initiate phosphorylation.
    • Output: 4 ATP produced (net gain of 2 ATP), 2 NADH, 2 pyruvate.
Aerobic Respiration
  • Breakdown of glucose in the presence of oxygen results in the production of 32 ATP molecules, CO₂, and H₂O.
  • Phases:
    1. Glycolysis
    2. Acetyl-CoA formation
    3. Citric acid cycle
    4. Electron-transport chain
Acetyl-CoA Formation
  • Pyruvate from glycolysis is converted into Acetyl-CoA in the mitochondrial matrix, releasing CO₂ and producing NADH.
Citric Acid Cycle
  • Also known as the Krebs cycle.
  • Acetyl-CoA combines with oxaloacetic acid, producing citric acid.
  • Results in ATP, NADH, FADH₂, and CO₂; oxaloacetic acid is regenerated, allowing the cycle to continue.
Electron-Transport Chain
  • Series of electron carriers in the inner mitochondrial membrane. High-energy electrons from NADH and FADH₂ pass through, generating a proton gradient.
  • Oxygen serves as the final electron acceptor, forming H₂O, while ATP synthase uses the proton gradient to generate ATP through chemiosmosis.
Summary of ATP Production


  • Processes:

ProcessATP ProducedOther Products
Glycolysis2 ATP2 NADH, 2 pyruvate
Acetyl-CoA Production0 ATP2 NADH
Citric Acid Cycle2 ATP6 NADH, 2 FADH₂
Electron-Transport Chain28 ATPH₂O
  • Total ATP from one glucose: 32 ATP.
  • Aerobic Respiration Equation:
    • C6H{12}O6 + 6O2 + 32ADP + 32Pi ightarrow 6CO2 + 6H_2O + 32 ATP
    Anaerobic Respiration
    • Occurs in the absence of oxygen, producing 2 ATP and 2 molecules of lactate.
    • Primarily occurs during intense exercise when oxygen is scarce.
    25.4 Lipid Metabolism
    • Triglycerides are broken down into free fatty acids and glycerol.
    • Free fatty acids enter the citric acid cycle after being converted to acetyl-CoA through beta-oxidation.
    • Ketogenesis: The conversion of acetyl-CoA into ketone bodies in the liver, which can also produce acidosis if excessive.
    25.5 Protein Metabolism
    • Amino Acid Identification:
      • Essential Amino Acids: Must be obtained through diet (9 total)
      • Nonessential Amino Acids: Synthesized by the body
    • Catabolism: Non-essential amino acids can undergo transamination and oxidative deamination, resulting in ammonia, which is converted into urea for excretion.
    25.6 Interconversion of Nutrient Molecules
    • Processes:
      • Glycogenesis: Converts excess glucose to glycogen.
      • Lipogenesis: Converts glucose and amino acids to lipids.
      • Glycogenolysis: Breakdown of glycogen to glucose.
      • Gluconeogenesis: Formation of glucose from amino acids and glycerol.
    25.7 Metabolic States
    • Absorptive State: Period immediately after eating; nutrients absorbed into the blood, and glucose is primarily used for energy.
    • Postabsorptive State: Occurs later when blood glucose levels must be maintained through the breakdown of stored energy (glycogen and triglycerides).
    Temperature Regulation
    • Heat Exchange Mechanisms:
      • Radiation: Heat energy emitted.
      • Evaporation: Loss of heat through sweating.
      • Conduction: Direct heat transfer from the body to cooler objects.
      • Convection: Heat loss through airflow around the body.
    • Normal Range Maintenance: Disturbances in body temperature evoke responses (like sweating or shivering) for regulatory purposes.