Overview
This lecture explains the importance of ATP as the universal energy carrier, how ATP is synthesized via phosphorylation in mitochondria and chloroplasts, and highlights similarities and differences in these processes.
ATP: Structure and Function
- ATP (adenosine triphosphate) is the universal energy currency of cells.
- ATP provides small, usable energy amounts for cellular reactions.
- Hydrolysis of ATP removes the terminal phosphate, releasing energy and forming ADP (adenosine diphosphate).
- ATP is easily regenerated from ADP by reattaching a phosphate group (phosphorylation).
ATP Synthesis: Phosphorylation and Chemiosmosis
- The enzyme ATP synthetase synthesizes ATP from ADP and inorganic phosphate (Pi).
- ATP synthetase is a membrane-bound enzyme.
- Energy for phosphorylation comes from a flow of protons (H+) down an electrochemical gradient via facilitated diffusion (chemiosmosis).
- High-energy electrons move through the electron transport chain, powering proton pumps and creating the gradient.
ATP Production in Mitochondria (Oxidative Phosphorylation)
- Hydrogen atoms from glycolysis, the link reaction, and Krebs cycle reduce NAD and FAD.
- Reduced NAD/FAD deliver electrons to the electron transport chain in the inner mitochondrial membrane.
- Proton pumps powered by these electrons move protons into the intermembrane space, creating an electrochemical gradient.
- Protons flow back through ATP synthetase; ATP is produced and water forms as oxygen acts as the final electron acceptor.
ATP Production in Chloroplasts (Photophosphorylation)
- The thylakoid membrane is the site of the electron transport chain during photosynthesis.
- Light excites electrons, which are passed along the chain, powering proton pumps that move protons into the thylakoid space.
- Protons flow through ATP synthetase back into the stroma, synthesizing ATP.
- NADP acts as the final electron acceptor, forming NADPH for the Calvin cycle.
Mitochondria vs. Chloroplasts: Comparison of Phosphorylation
- Both processes rely on an electron transport chain to create an electrochemical gradient for ATP production via chemiosmosis.
- Mitochondria use breakdown of glucose (respiration), inner mitochondrial membrane, 3 proton pumps, oxygen as final electron acceptor, protons flow from inter-membrane space into matrix.
- Chloroplasts use photons (light), thylakoid membrane, 1 proton pump, NADP as final electron acceptor, protons flow from thylakoid space into stroma.
Key Terms & Definitions
- ATP (Adenosine Triphosphate) — Universal energy-carrying molecule in cells.
- ADP (Adenosine Diphosphate) — Formed when ATP loses a phosphate group.
- Phosphorylation — Adding a phosphate group to a molecule, here to ADP to form ATP.
- ATP synthetase — Membrane-bound enzyme synthesizing ATP.
- Chemiosmosis — Movement of protons down an electrochemical gradient to generate ATP.
- Electron Transport Chain — Series of protein complexes transferring electrons, powering proton pumps.
- Oxidative Phosphorylation — ATP formation in mitochondria using energy from respiration.
- Photophosphorylation — ATP production in chloroplasts using energy from light.
Action Items / Next Steps
- Review diagrams of ATP synthesis in mitochondria and chloroplasts.
- Study key differences and similarities between oxidative and photophosphorylation.