Lecture Notes: Cellular Respiration and Fermentation

Background and Personal Anecdote

• Lecturer's childhood love for swimming.
• Early misconception about fish and oxygen.
• Realization of the importance of oxygen for most organisms.

Importance of Oxygen

• Essential for many organisms: fish, plants, humans.
• Plants need oxygen for cellular respiration, despite producing oxygen during photosynthesis.

Cellular Respiration

Why Do Organisms Need Oxygen?

• Oxygen is required for cellular respiration to produce ATP.
• ATP (adenosine triphosphate): powers many cellular processes.
• ADP (adenosine diphosphate) can be converted back to ATP.

Aerobic Cellular Respiration

• Requires oxygen.
• Complex process with several steps (glycolysis, Kreb's cycle, and electron transport chain).

What Happens When There Is No Oxygen?

Types of Cells That Can Handle Lack of Oxygen

• Many types of bacteria, archaea, yeast, and muscle cells.

Anaerobic Respiration

• Some organisms perform anaerobic respiration, continuing glycolysis and Kreb's cycle without oxygen.
• Use alternative electron acceptors like sulfate.

Fermentation

• A way to produce ATP when oxygen is not present.
• Allows glycolysis to continue by regenerating NAD+.

Glycolysis Recap

• Glucose converted to pyruvate.
• Produces 2 net ATP and 2 NADH.
• NAD+ reduced to NADH (oxidation-reduction process).

Types of Fermentation

Alcoholic Fermentation

• Done by some yeasts.
• Produces ethanol and carbon dioxide.
• Acetaldehyde acts as an electron acceptor to regenerate NAD+.
• Used in bread making (alcohol evaporates during baking).

Lactic Acid Fermentation

• Done by muscle cells during oxygen debt or intense exercise.
• Produces lactate from pyruvate.
• Pyruvate acts as an electron acceptor to regenerate NAD+.
• Recent research suggests lactate might not cause muscle soreness.

Applications of Fermentation

• Lactic acid fermentation in yogurt production.
• Alcoholic fermentation in bread and alcohol production.

Conclusion

• Fermentation is remarkable but not as efficient as aerobic respiration.
• Emphasis on the importance of oxygen for maximum ATP production.

Stay Curious!