PHR1031 AC3.1 Energy Metabolism (Lecturer AP) 2025

Energy Metabolism Overview

  • Metabolism Basics

    • Metabolism provides energy for bodily functions and is essential for understanding metabolic disorders.

    • Key disorders include:

      • Glycogen storage diseases

      • Mitochondrial disorders

      • Diabetes

Energy Sources

  • Fuel Types

    • Cells use glucose and fats to generate energy.

    • Carbohydrate and lipid metabolic pathways are regulated daily.

    • Understanding the impact of disrupted metabolic pathways is crucial for predicting physiological and clinical consequences.

Key Metabolic Pathways

Glycolysis

  • Purpose: Breakdown of glucose to pyruvate, producing ATP and NADH.

  • Location: Occurs in the cytoplasm.

  • Inputs: Glucose.

  • Outputs: 2 Pyruvate, 2 ATP, 2 NADH.

Citric Acid Cycle (Krebs Cycle)

  • Purpose: Processes acetyl CoA to produce NADH, FADH2, and GTP.

  • Location: Mitochondrial matrix.

  • Inputs: Acetyl CoA from glycolysis.

  • Outputs: CO2, NADH, FADH2, GTP.

Oxidative Phosphorylation

  • Purpose: Use of NADH and FADH2 to drive ATP synthesis via electron transport chain (ETC).

  • Location: Inner mitochondrial membrane.

  • Inputs: NADH, FADH2, O2.

  • Outputs: ATP, H2O.

Fatty Acid Oxidation

  • Purpose: Break down fatty acids into acetyl CoA units for energy.

  • Location: Mitochondria in most cells.

  • Inputs: Fatty acids.

  • Outputs: Acetyl CoA, NADH, and FADH2.

Review Questions

  • Citric Acid Cycle Products:

    • Not a product: Acetyl CoA (it enters the cycle, but is not a product).

    • Products include: CO2, NADH, GTP, and FADH2.

Energy Pathway Disruption

  • Poisons and Toxicity:

    • Rotenone: Inhibits NADH dehydrogenase in the ETC, halting ATP production.

    • Antimycin A: Inhibits ubiquinone oxidation, blocking electron transport.

    • Malonate: Competitive inhibitor of succinate dehydrogenase, affecting citric acid cycle.

    • Detection of Blockages: Through measurement of ATP production, changes in metabolite levels, and functional assays.

Energy Utilization in Different Cell Types

  • Hepatocytes: Utilize glucose, proteins, and triglycerides.

  • Erythrocytes: Primarily rely on glucose.

  • Macrophages: Use glucose, minimal protein utilization.

  • Nerve Cells: Prefer glucose, oxidative metabolism.

  • Adipocytes: Process glucose and triglycerides.

  • Myocytes: Use glucose predominantly during exercise.

Glycolysis Assessment

  • Definition: Glycolysis refers to the breakdown of glucose to pyruvate, not to be confused with processes involving glycerol or carbon dioxide synthesis.

Final Thoughts

  • Understanding the connectivity among different metabolic pathways is crucial for both clinical applications and the study of metabolism.