Lecture Notes on Cellular Respiration and Fermentation

Introduction

• Speaker shares personal experience with swimming and misconceptions about fish and oxygen.
• Emphasizes the importance of oxygen for various organisms (fish, plants, and humans).

Importance of Oxygen

• Oxygen is essential for cellular respiration in all living organisms.
• Even plants, which produce oxygen, require it for cellular respiration.
• Cellular Respiration Formula: Oxygen is a reactant in breaking down glucose to form ATP.

What is ATP?

• ATP: Adenosine Triphosphate, a high-energy molecule with three phosphates.
• Powers many cellular processes; when losing a phosphate, it converts to ADP (Adenosine Diphosphate).
• Enzymes can convert ADP back to ATP in cellular respiration.

Aerobic vs. Anaerobic Respiration

• Aerobic Respiration: Requires oxygen; involves complex processes (glycolysis, Krebs cycle, electron transport chain).
• Anaerobic Respiration: Occurs without oxygen; some cells can adapt (e.g., bacteria, yeast, muscle cells).

Types of Cells that Can Handle Low Oxygen

• Certain bacteria and archaea.
• Yeast (e.g., used in bread making).
• Muscle cells can survive without oxygen temporarily.

Anaerobic Processes

• Some bacteria and archaea can perform anaerobic respiration using alternative electron acceptors (e.g., sulfate).
• Alternatively, organisms can undergo fermentation to regenerate NAD+ and continue glycolysis.

What is Fermentation?

• Fermentation allows glycolysis to continue in the absence of oxygen, yielding ATP.
• Less efficient than aerobic respiration (produces less ATP).

Glycolysis Overview

• Glucose is converted into pyruvate during glycolysis.
• Yields 2 net ATP and 2 NADH.
• Understanding the role of NADH and NAD+ in these processes:
  • NADH: Electron carrier, gains electrons to become NADH from NAD+ (reduction).
  • NAD+: Needs to be regenerated for glycolysis to continue.

Types of Fermentation

1. Alcoholic Fermentation

• Conducted by yeast.
• Glycolysis produces 2 pyruvate, 2 ATP, and 2 NADH.
• Pyruvate is converted into acetaldehyde (electron acceptor) which helps oxidize NADH back to NAD+.
• Produces carbon dioxide and ethanol (alcohol) as waste products.
• Carbon dioxide helps bread to rise; alcohol evaporates during baking.

2. Lactic Acid Fermentation

• Occurs in muscle cells during oxygen debt (intense exercise).
• Glycolysis results in the same products as alcoholic fermentation.
• Pyruvate acts as an electron acceptor, leading to the production of lactate.
• Lactate has been traditionally blamed for muscle soreness, but recent research may dispute this.
• Also occurs in bacteria involved in yogurt production, contributing to its sour taste.

Conclusion

• Fermentation is an essential process for survival in low oxygen conditions.
• While it is a remarkable process, it cannot match the ATP production of aerobic respiration.
• Encouragement to stay curious and seek further understanding of these biological processes.