Overview
This lecture explains how cells produce energy with and without oxygen, focusing on fermentation as an alternative to aerobic respiration and detailing alcoholic and lactic acid fermentation.
The Role of Oxygen in Cellular Respiration
- Oxygen is necessary for aerobic cellular respiration in most organisms, including plants, animals, and some bacteria.
- Plants also need oxygen for cellular respiration despite producing it during photosynthesis.
- Oxygen acts as a vital reactant, allowing for the efficient breakdown of glucose into ATP.
ATP and Its Importance
- ATP (adenosine triphosphate) is the main energy currency of the cell, used to power many cellular processes.
- When ATP loses a phosphate, it becomes ADP (adenosine diphosphate), which can be recycled back to ATP during respiration.
Cellular Respiration and Glycolysis
- Aerobic respiration involves glycolysis, Krebs cycle, and the electron transport chain, requiring oxygen as the final electron acceptor.
- Glycolysis (occurring in cytoplasm) breaks glucose into pyruvate, producing 2 net ATP and 2 NADH per glucose.
Anaerobic Respiration and Fermentation
- Some bacteria, archaea, yeast, and muscle cells can survive without oxygen using anaerobic respiration or fermentation.
- Anaerobic respiration uses a different final electron acceptor (like sulfate) instead of oxygen.
- Fermentation allows glycolysis to continue in the absence of oxygen by regenerating NAD+ from NADH.
Types of Fermentation
- Alcoholic Fermentation: Done by yeast; converts pyruvate to ethanol and CO₂, using acetaldehyde as electron acceptor to regenerate NAD+.
- Lactic Acid Fermentation: Occurs in muscle cells and some bacteria; converts pyruvate to lactate, using pyruvate as electron acceptor to regenerate NAD+.
- Both types yield 2 ATP per glucose, much less than aerobic respiration.
Real-Life Applications and Misconceptions
- Muscle cells switch to lactic acid fermentation when oxygen is scarce (e.g., intense exercise).
- Lactic acid, produced in fermentation, may not directly cause post-exercise muscle soreness.
- Fermentation is also used in making bread, yogurt, and other foods.
Key Terms & Definitions
- Aerobic Respiration — Process using oxygen to produce ATP from glucose.
- Anaerobic Respiration — Energy production using other molecules instead of oxygen as final electron acceptor.
- Fermentation — Process that enables glycolysis to continue without oxygen by regenerating NAD+.
- Glycolysis — First step in glucose breakdown, produces pyruvate, ATP, and NADH.
- NAD+/NADH — Electron carrier molecule; NAD+ accepts electrons to become NADH.
- ATP (Adenosine Triphosphate) — Main energy carrier in cells.
Action Items / Next Steps
- Review the detailed steps of glycolysis, alcoholic, and lactic acid fermentation.
- Check suggested readings on the role of lactic acid in muscle soreness.