Overview
This lecture covers the process of cellular respiration, the main pathway by which cells convert glucose into usable energy (ATP), and summarizes its main stages and products.
Importance of Cellular Respiration
- Cellular respiration is the process that converts glucose into usable energy for the cell.
- Most carbohydrates from food are converted to glucose for this process.
- The main products are ATP (energy), carbon dioxide, and water.
Overall Chemical Reaction
- The simplified equation: C₆H₁₂O₆ (glucose) + 6O₂ → 6CO₂ + 6H₂O + energy (mainly in ATP).
- Textbooks often state 1 glucose yields 38 ATP, but real values can range from 29–30 ATP.
Stages of Cellular Respiration
- Cellular respiration consists of three main stages: glycolysis, Krebs cycle, and electron transport chain.
Glycolysis
- Glycolysis breaks one 6-carbon glucose molecule into two 3-carbon pyruvate molecules.
- Occurs without oxygen (anaerobic).
- Uses 2 ATP, produces 4 ATP; net gain is 2 ATP.
- Generates NADH for later stages.
Krebs Cycle (Citric Acid Cycle)
- Follows glycolysis only if oxygen is present (aerobic).
- Each glucose leads to two turns of the cycle, forming 2 ATP total.
- Produces more NADH and FADH₂ for use in the electron transport chain.
Electron Transport Chain (ETC)
- Requires oxygen (aerobic).
- Bulk of ATP production: up to 34 ATP per glucose in ideal conditions.
- NADH and FADH₂ donate electrons to power ATP synthesis.
Alternative Pathways
- If oxygen is absent, cellular respiration cannot proceed past glycolysis.
- Pyruvate is converted by fermentation: lactic acid (in humans/mammals) or alcohol (in yeast).
Key Terms & Definitions
- Cellular Respiration — Process converting glucose and oxygen to ATP, CO₂, and H₂O.
- ATP (Adenosine Triphosphate) — Main energy currency of the cell.
- Glycolysis — Anaerobic process splitting glucose into two pyruvate, producing ATP and NADH.
- Krebs Cycle — Aerobic cycle breaking down pyruvate, producing ATP, NADH, and FADH₂.
- Electron Transport Chain (ETC) — Series of proteins using NADH and FADH₂ to generate ATP.
- Anaerobic — Does not require oxygen.
- Aerobic — Requires oxygen.
- Fermentation — Anaerobic process converting pyruvate to lactic acid (humans) or alcohol (yeast).
- NADH / FADH₂ — Molecules transporting electrons to the ETC for ATP production.
Action Items / Next Steps
- Review detailed stages of glycolysis, Krebs cycle, and electron transport chain in upcoming materials.