Structure of chlorophyll molecule

1. Structure of chlorophyll molecule • Long, non-polar hydrophobic “tail” anchors in lamellar membranes • Bound to membranes • “head” has a complex ring with Mg2+ at center • Where light energy is trapped

2. Accessory Pigments • Absorb wavelengths that chlorophyll can’t • Pass along energy into photosynthetic process  plants more efficient this way • Do not waste wavelengths

3. Accessory Pigments • Phycobilins • Found in red algae & blue-green bacteria • Phycoerythrin: (red) max absorption @ 550 nm • Phycocyanin: (blue) max absorption @ 620 nm

4. Accessory Pigments • Carotenoids • Protect chlorophylls from damage by bright light • Take in certain λ, transfer energy to chlorophyll a

6. Light Reactions • Overview • System I responds to λ of 700 nm • Molecule is called P700 • System II responds to λ of about 680 nm • Molecule is called P680 • BOTH reactions (both λ) are necessary for photosynthesis

8. Electron Transport ChainLight Reactions • Photosystem I • 700 nm light strikes P700 • 2e- released • NADP+ reduced to NADPH (stored in stroma) • NADPH contains energy

9. Electron Transport ChainLight Reactions • Photosystem II • 680 nm light strikes P680 • H2O splits, O2 released • 2e- released • e- goes to plastiquinone • e- transferred to ETC • Pumps H into lumen

11. Electron Transport ChainLight Reactions • Manganese (Mn)-complex give electrons back to P680 by splitting 2 water molecules • 4 photons need to split 2 water molecules

12. Summary: Light Reactions • NADPH stored in stroma • H+ pumped into thylakoid reservoir (lumen) • Creates electrochemical gradient for ATP synthesis

13. thylakoid membrane Chemiosmotic Theory of ATP formation (noncyclic flow) H+ H+ H+ H+ H+ H+ H+ H+ H+ H+ NADP+ PSII PSI NADPH lumen ATP synthase stroma ATP ADP

14. Cyclic flow