Overview
This lecture introduces cellular respiration, focusing on how glucose is metabolized through a series of small steps to generate ATP, the primary energy currency of the cell.
Introduction to Cellular Respiration
- Cellular respiration is the breakdown of glucose to release and capture energy in the form of ATP.
- The overall chemical equation is: glucose + oxygen → carbon dioxide + water + ATP.
- Energy is stored in glucose's carbon-carbon bonds; breaking these releases usable energy.
- Cellular respiration consists of many small steps to efficiently capture energy and minimize loss as heat.
Electron Carriers and Redox Reactions
- High energy electron carriers like NAD+ (becomes NADH) and FAD (becomes FADH2) capture and transfer electrons in cellular respiration.
- Redox (reduction-oxidation) reactions involve electron transfer: oxidation is loss of electrons, reduction is gain of electrons (use mnemonic OIL RIG or LEO the lion says GER).
- Reducing agents donate electrons; oxidizing agents accept electrons.
ATP and Energy Transfer
- ATP (adenosine triphosphate) is hydrolyzed to ADP (adenosine diphosphate) and Pi, releasing energy for cellular work.
- Removing a phosphate group (dephosphorylation) releases energy; adding a phosphate (phosphorylation) makes molecules more reactive, often done by kinases.
- NADH acts like an energy ticket, later traded in to make ATP.
Methods of ATP Production
- Substrate-level phosphorylation transfers a phosphate directly from a substrate to ADP to form ATP.
- Chemiosmosis produces most ATP, using ATP synthase and occurring mainly in mitochondria (or plasma membrane in prokaryotes).
Glycolysis: The First Step of Cellular Respiration
- Glycolysis splits a 6-carbon glucose into two 3-carbon pyruvate molecules in ten steps.
- Inputs: glucose, NAD+, ATP, ADP. Outputs: pyruvate, NADH, ATP, ADP.
- The first five steps (investment phase) use ATP; the last five steps (payoff phase) generate a net gain of 2 ATP and 2 NADH.
- ATP in glycolysis is produced by substrate-level phosphorylation.
- Glycolysis occurs in the cytoplasm and does not require oxygen (anaerobic).
Regulation of Glycolysis
- Glycolysis is regulated by trapping glucose in the cell and by the availability of NAD+ and ATP.
- High ATP levels or limited NAD+ slow or stop glycolysis.
Key Terms & Definitions
- Cellular Respiration — Metabolic process breaking down glucose to make ATP.
- ATP (Adenosine Triphosphate) — Main energy carrier in cells.
- NAD+/NADH, FAD/FADH2 — Electron carriers in their oxidized/reduced forms.
- Redox Reaction — Chemical reaction transferring electrons between molecules.
- Phosphorylation — Addition of a phosphate group to a molecule.
- Substrate-level Phosphorylation — Direct transfer of phosphate from substrate to ADP.
- Chemiosmosis — ATP generation using a proton gradient and ATP synthase.
- Glycolysis — Metabolic pathway splitting glucose into two pyruvates.
Action Items / Next Steps
- Review optional video links provided in the textbook for deeper understanding of metabolic pathways.
- Prepare for the next lecture covering post-glycolysis pathways.