Lecture on Cellular Respiration

Overview

• Cellular respiration derives energy from food.
• Reactants: Glucose (C6H12O6) and oxygen.
• Products: Carbon dioxide, water, and energy (ATP).
• Exergonic process releasing energy efficiently as ATP.

Importance of ATP

• ATP (Adenosine Triphosphate) is the energy currency of the cell.
• ATP drives endergonic reactions through phosphate group transfer.
• ATP provides energy more efficiently than direct glucose use.
• Structure of ATP: Comprises a ribose sugar, adenine, and three phosphate groups.

Stages of Cellular Respiration

1. Glycolysis

   • Occurs in the cytosol.
   • Splits glucose into two pyruvate molecules.
   • Produces a net gain of 2 ATP and 2 NADH through substrate-level phosphorylation.
   • Involves investment and payoff phases.

2. Pyruvate Oxidation

   • Occurs in the mitochondrial matrix.
   • Converts pyruvate to acetyl CoA, releasing CO2 and producing NADH.

3. Krebs Cycle (Citric Acid Cycle)

   • Occurs in the mitochondrial matrix.
   • Acetyl CoA is oxidized to CO2.
   • Produces NADH, FADH2, and ATP.

4. Electron Transport Chain (ETC) and Chemiosmosis

   • Located in the inner mitochondrial membrane.
   • Electrons from NADH and FADH2 pass through complexes, producing ATP.
   • Oxygen acts as the final electron acceptor, forming water.

Key Concepts

• Phosphorylation

  • Substrate-level phosphorylation: Direct ATP formation in glycolysis and Krebs cycle.
  • Oxidative phosphorylation: ATP formation during ETC and chemiosmosis.

• Enzymes Involved

  • Kinase: Transfers phosphate groups.
  • Dehydrogenase: Facilitates oxidation-reduction reactions.
  • Isomerase: Catalyzes structural rearrangements.

Energy Yield

• Maximum theoretical ATP yield: 36-38 ATP per glucose.
• Efficiency varies due to potential losses and transport costs.

Anaerobic Conditions

• Fermentation
  • Lactic acid fermentation in muscle cells.
  • Ethanol fermentation in yeast cells.
  • Allows ATP production in absence of oxygen through regeneration of NAD+.

Comparisons and Examples

• Combustion engine analogy: Efficient energy conversion by releasing energy gradually.
• Importance of electron acceptors: Oxygen's high electronegativity drives electron transport.

Study Tips

• Understand locations of each stage in the cell and the role of different enzymes.
• Memorize key products and inputs of each stage.
• Practice with questions to test understanding of processes and concepts.

Test Review Questions

1. Identify products of cellular respiration.
2. Understand differences between aerobic and anaerobic processes.
3. Clarify enzyme functions and roles in reactions.
4. Know the ATP yield and stages that contribute to it.

This lecture provides a detailed look into cellular respiration, crucial for understanding energy production in biological systems.