Cellular Respiration Overview

Importance of Cellular Respiration

• All cells require energy continuously, primarily derived from ATP.

• The methods of ATP production depend on oxygen availability and biological characteristics of the cell.

• Examples of oxygen-rich environments include normal human activities, while anaerobic processes are observed in yeast and certain bacteria.

Phases of Cellular Respiration

1. Glycolysis

   • Occurs in the cytoplasm.

   • Converts glucose into pyruvate, produces 2 ATP and 2 NADH.

2. Link Reaction

   • Takes place in mitochondria. Converts pyruvate to acetyl-CoA, producing CO2 and NADH.

3. Krebs Cycle

   • Occurs in mitochondria, processes acetyl-CoA, produces ATP, NADH, FADH2, and CO2.

4. Oxidative Phosphorylation

   • Occurs in mitochondria, uses NADH and FADH2 to produce large amounts of ATP and water. Requires oxygen as the final electron acceptor.

Chemical Process

• Overall process:C6H12O6 + 6O2 → 6CO2 + 6H2O + Energy

• Reactants:

  • Glucose and oxygen.

• Products:

  • Carbon dioxide, water, and ATP.

ATP Production

• The primary purpose of cellular respiration is to provide energy (ATP) to cells.

• Total ATP produced per glucose: approximately 38 ATP (but can vary based on conditions).

High Potential Energy Molecules

• Other than ATP, NADH and FADH2 are important free energy carriers in cellular respiration.

• They transport high-energy electrons to the electron transport chain during oxidative phosphorylation.

Electron Transport and Coenzymes

• NAD+ and FAD are coenzymes that facilitate electron transfer.

• They become reduced to NADH and FADH2 during glycolysis and Krebs Cycle.

• Oxygen accepts electrons at the end of the electron transport chain, forming water.

• Oxidation-Reduction Reactions:

  • Oxidation: loss of electrons (e.g., glucose).

  • Reduction: gain of electrons (e.g., NAD+ to NADH).

Anaerobic Respiration

• Anaerobic processes do not require oxygen and include fermentation (e.g., lactic acid or alcohol fermentation).

• Glycolysis produces 2 ATP per glucose, but little efficiency compared to aerobic respiration.

• The fermentation process regenerates NAD+ for glycolysis to continue under low oxygen conditions.

Summary of Cellular Processes

• Energy/Adenosine Triphosphate (ATP) is necessary for various cellular activities (e.g., muscle contraction, nerve impulse transmission).

• Lactic acid buildup during vigorous exercise causes the "burn" felt in muscles due to anaerobic metabolism when oxygen is limited.

Evolutionary Implications

• Oxygen-dependent organisms gained an evolutionary advantage, leading to diversification of life forms in an oxygen-rich environment.