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Understanding the Oxidative Energy System

Sep 5, 2024

Bioenergetics Lecture Notes

Overview

  • Lecture focuses on the oxidative energy system and its role in bioenergetics.
  • Comparison with previously covered systems: ATP-PC system and glycolysis.

ATP-PC System

  • Uses phosphocreatine to synthesize ATP.
  • Creatine kinase is the primary enzyme.
  • Produces 1 ATP per phosphocreatine.

Glycolysis

  • Breakdown of glucose or glycogen.
  • 12-step chemical reaction cascade.
  • Rate-limiting enzyme: Phosphofructokinase (PFK).
  • Produces ATP, NADH, and 2 pyruvates.
    • Pyruvates can become lactate in anaerobic conditions.
    • In presence of oxygen, they continue in the oxidative system.

Oxidative System

  • Aerobic energy system requiring oxygen.
  • Higher ATP yield compared to other systems:
    • 32-33 ATP from one glucose.

    • 100 ATP from fatty acids.

Characteristics

  • Duration: 2 minutes to infinity.
  • Suitable for long-duration, low-intensity exercises.
  • Slower than ATP-PC and glycolysis but yields more ATP.
  • Reactions occur in mitochondria ("powerhouse of the cell").

Oxidation of Carbohydrates

  1. Glycolysis: Produces pyruvate, ATP, and NADH.
  2. Conversion to Acetyl-CoA: Pyruvate converts to Acetyl-CoA in presence of oxygen.
  3. Krebs Cycle: Acetyl-CoA enters Krebs cycle.
    • Produces NADH, FADH, ATP, and CO2.
    • Rate-limiting enzyme: Isocitrate dehydrogenase.

Krebs Cycle Outputs

  • 2 Acetyl-CoA yield:
    • 6 NADH
    • 2 FADH
    • 2 ATP
    • Water and CO2

Electron Transport Chain

  • NADH and FADH deliver electrons.
  • Cytochromes process hydrogens and electrons.
  • Oxygen is the final electron acceptor.
  • ATP synthesized primarily here:
    • 2.5 ATP per NADH
    • 1.5 ATP per FADH

Total ATP Yield from Glucose

  • Glycolysis: Net of 2 ATP.
  • Conversion to Acetyl-CoA: 5 ATP.
  • Krebs Cycle: 15 ATP from NADH, 3 ATP from FADH, 2 ATP via substrate phosphorylation.
  • Total for glucose: 32 ATP.
  • Total for glycogen: 33 ATP.

Summary

  • Oxidative phosphorylation yields significant energy for long durations.
  • Involves complex processes, including glycolysis, Krebs cycle, and electron transport chain, primarily in mitochondria.

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