Aerobic vs. Anaerobic Respiration

Overview

• Aerobic Respiration: Occurs in the presence of oxygen.
• Anaerobic Respiration: Occurs without oxygen.
• Cellular Respiration: Converts glucose into carbon dioxide and water (aerobic process).

Aerobic Respiration

1. Glycolysis
   • Converts glucose into pyruvate.
   • Does not require oxygen.
2. Pyruvate Oxidation
   • Pyruvate converted into acetyl enzyme A (acetyl-CoA).
3. Krebs Cycle (Citric Acid Cycle)
   • Acetyl-CoA oxidized to CO2.
   • Electrons used to reduce NAD+ to NADH and FAD to FADH2.
4. Electron Transport Chain
   • NADH and FADH2 donate electrons to oxygen, forming water.

Chemical Equation

• Overall Equation: C6H12O6 + 6O2 -> 6CO2 + 6H2O
• Yields:
  • 2 pyruvate molecules per glucose.
  • 2 CO2 molecules from pyruvate oxidation.
  • 4 CO2 molecules from the Krebs cycle.

Anaerobic Respiration

Types

1. Ethanol Fermentation

   • Common in yeast.
   • Process:
     1. Glycolysis: Glucose -> 2 pyruvate (produces 2 ATP).
     2. Pyruvate -> 2 acetaldehyde (via decarboxylation, releasing CO2).
     3. Acetaldehyde reduced to ethanol (NADH oxidized to NAD+).
   • End Product: Ethanol.

2. Lactic Acid Fermentation

   • Occurs in muscle cells.
   • Process:
     1. Glycolysis: Glucose -> 2 pyruvate (produces 2 ATP).
     2. Pyruvate reduced to lactate (NADH oxidized to NAD+).
   • End Product: Lactate.

Key Points

• ATP Yield:
  • Both ethanol and lactic acid fermentation yield 2 ATP per glucose.
  • Aerobic respiration yields up to 36-38 ATP per glucose.
• NAD+ Regeneration:
  • Essential for glycolysis to continue in anaerobic conditions.

Review Questions

1. ATP Yield in Lactic Acid Fermentation: 2 ATP.
2. False Statement: Lactic acid fermentation produces CO2 (it does not).

Summary

• Aerobic Respiration: With oxygen, yields high ATP.
• Anaerobic Respiration: Without oxygen, includes ethanol and lactic acid fermentation. Both yield 2 ATP per glucose.