Overview
This lecture covers the four main steps of cellular respiration, focusing on glycolysis, the prep step, the Krebs cycle, and the electron transport chain, including key molecules, locations, and energy production.
Glycolysis
- Glycolysis is the first step in cellular respiration and takes place in the cytoplasm.
- It involves breaking one glucose molecule (6 carbons) into two pyruvate molecules (3 carbons each).
- No oxygen is required; glycolysis is anaerobic.
- Net production is 2 ATP and 2 NADH per glucose.
- NAD+ (from vitamin B3, niacin) picks up hydrogen to form NADH.
Prep Step (Pyruvate Oxidation)
- The prep step converts pyruvate (3 carbons) into acetyl CoA (2 carbons) and releases CO₂.
- This step takes place in the mitochondria.
- No ATP is made in this step; more NADH is produced as electrons and hydrogens are captured.
Krebs Cycle (Citric Acid Cycle)
- Acetyl CoA enters the Krebs cycle in the mitochondria.
- The acetyl group (2 carbons) combines with a 4-carbon molecule to form citric acid (6 carbons).
- Carbons are removed as CO₂, regenerating the 4-carbon starter.
- Each turn produces 1 ATP, 3 NADH, 1 FADH₂, and releases 2 CO₂; cycle runs twice per glucose.
Electron Transport Chain (ETC)
- The ETC is located on the inner mitochondrial membrane (cristae).
- NADH and FADH₂ drop off electrons, which create a proton (H⁺) gradient.
- ATP synthase uses the proton motive force to convert ADP to ATP.
- Oxygen is the final electron acceptor, forming water with hydrogen ions.
- This step produces 32 ATP and is called oxidative phosphorylation.
Key Terms & Definitions
- Glycolysis — Breakdown of glucose into two pyruvate molecules, producing ATP and NADH.
- Anaerobic — Process that occurs without oxygen.
- NAD⁺/NADH — Electron carrier; NAD⁺ becomes NADH when it picks up electrons/hydrogen.
- Pyruvate — Three-carbon molecule formed from glucose in glycolysis.
- Acetyl CoA — Two-carbon molecule entering the Krebs cycle.
- Krebs Cycle — Series of reactions that generates ATP, NADH, FADH₂, and CO₂ from acetyl CoA.
- Electron Transport Chain (ETC) — Series of proteins that transfer electrons and create ATP using oxygen.
- ATP Synthase — Enzyme that synthesizes ATP using the proton gradient.
- Oxidative Phosphorylation — ATP formation process using oxygen as the final electron acceptor.
Action Items / Next Steps
- Review the main steps and their locations in the cell.
- Memorize key reactants, products, and ATP yield for each step.
- Be prepared to identify which steps are aerobic and anaerobic.