An Introduction to Chemiosmosis

1. An Introduction to Chemiosmosis

2. Electron Transport Overview Electrons pass through a non-cyclic electron transport chain and provide energy to pump H+ ions from the stroma, across the thylakoid membrane to the thylakoid compartment.

3. Chemiosmosis • Chemiosmosis: Source of ATP production in photophosphorylation.

4. Takes place in Chloroplasts in the thylakoid.

5. Photosystem II The energy from the photon is captured by a pigment molecule from the photosystem. This energy is passed to other pigments until it reaches the chlorophyll molecule. Light energy is used to oxidize water and this produces electrons, protons (H+) and oxygen gas. The chlorophyll molecule is oxidized and carries a positive charge. Therefore the electron acceptor is reduced.

6. Redox Reactions in Thylakoid Membrane • Excited electrons reduce plastoquinone, an electron acceptor. • The energy moves H+ ions across the membrane into the thylakoid interior. • Plastoquinone is oxidized and electrons move to cytochrome, which is reduced. • Cytochrome passes the electrons to plastocyanin making cytochrome oxidized and plastocyanin reduced.

7. Redox Reactions

8. Photosystem I • Absorbs light energy, and each photon donates an electron to electron acceptor, which in this case is ferredoxin

9. NADP Reductase • Reduced ferredoxin donates two electrons to NADP reductase • Also takes two H+ from stroma thereby reducing NADP+ to NADPH+H+

10. ATP Synthesis • Due to the pH difference, H+ ions diffuse back to the stroma through ATP synthase channels and form ATP from ADP + P • The production of ATP through the use of proton gradient is called photophosphorylation or chemiosmosis

11. Overview of Chemiosmosis • http://bcs.whfreeman.com/thelifewire/content/chp08/0802002.html