Overview
This lecture explains aerobic cellular respiration in eukaryotic cells, detailing how ATP is produced through a series of steps involving glucose breakdown.
Introduction to Cellular Respiration
- Cells need ATP (adenosine triphosphate) as their main energy currency.
- Both prokaryotic and eukaryotic cells must make ATP, but the processes can differ.
- Aerobic cellular respiration is focused on eukaryotic cells with mitochondria.
Cellular Respiration Equation & Comparison to Photosynthesis
- The overall equation for aerobic respiration involves glucose and oxygen as reactants, and carbon dioxide, water, and ATP as products.
- The equation for cellular respiration is similar to, but not the reverse of, photosynthesis.
- Plants can perform both photosynthesis (make glucose) and cellular respiration (break down glucose).
Step 1: Glycolysis
- Occurs in the cytoplasm and is anaerobic (no oxygen required).
- Glucose is converted to 2 pyruvate, yielding a net of 2 ATP and 2 NADH.
- NADH is a coenzyme that transfers electrons needed later.
Intermediate Step: Pyruvate to Acetyl CoA
- Pyruvate is actively transported to the mitochondrial matrix and oxidized to 2 acetyl CoA.
- This step produces 2 NADH and releases carbon dioxide.
Step 2: Krebs Cycle (Citric Acid Cycle)
- Takes place in the mitochondrial matrix; requires oxygen indirectly (aerobic).
- Each acetyl CoA is further broken down, releasing carbon dioxide.
- Produces 2 ATP, 6 NADH, and 2 FADH2 (another electron-carrying coenzyme).
Step 3: Electron Transport Chain & Chemiosmosis
- Occurs on the inner mitochondrial membrane.
- NADH and FADH2 donate electrons to protein complexes, creating a proton gradient across the membrane.
- Protons flow through ATP synthase, powering ATP production from ADP.
- Oxygen acts as the final electron acceptor, forming water.
- This step produces the most ATP (estimates: 26–34 ATP per glucose).
ATP Yield & Variability
- Total ATP yield from all steps can range between 30 and 38 ATP per glucose molecule.
- Yield varies due to factors like the proton gradient and cellular conditions.
Alternative Pathways & Importance of ATP Production
- Fermentation produces ATP when oxygen is unavailable but is less efficient.
- Blocking ATP production (e.g., by cyanide) can be lethal.
- Research continues on mitochondrial diseases linked to faulty ATP production.
Key Terms & Definitions
- ATP (Adenosine Triphosphate) — Primary energy currency of the cell.
- Glycolysis — First step of respiration; breaks glucose into pyruvate.
- NADH/FADH2 — Coenzymes that carry electrons to the electron transport chain.
- Krebs Cycle (Citric Acid Cycle) — Series of reactions in mitochondrial matrix generating energy carriers.
- Electron Transport Chain — Series of proteins that use electrons to create a proton gradient and produce ATP.
- Chemiosmosis — Movement of protons through ATP synthase to generate ATP.
- Fermentation — Anaerobic process that generates ATP without oxygen.
Action Items / Next Steps
- Review the detailed steps and outputs of glycolysis, Krebs cycle, and electron transport chain.
- Check recommended readings for more information on the Krebs cycle and ATP yield variability.
- Watch suggested videos on ATP, cell transport, and fermentation.