photosystem Iand II,ETC

Botanyphycology

1. PRESENTED TO; MAM RABIA PRESENTED BY; AZKA JAVED

2. TOPIC PHOTOSYSTEM I & II ELECTRON TRANSPOT CHAIN

3. Chloroplasts absorb light energy and convert it to chemical energy Light Reflected light Absorbed light Transmitted light Chloroplast THE COLOR OF LIGHT SEEN IS THE COLOR NOT ABSORBED

4. Photosynthesis is the process by which autotrophic organisms use light energy to make sugar and oxygen gas from carbon dioxide and water AN OVERVIEW OF PHOTOSYNTHESIS Carbon dioxide Water Glucose Oxygen gas PHOTOSYNTHESIS

5. Photosystem : Reaction center surrounded by several light-harvesting complexes Light-harvesting complex : P igment molecules bound to proteins (act as antenna for reaction center ) Photosystems

6. Reaction center : Protein complex that includes 2 special chlorophyll a molecules + primary e- acceptor molecule First step of light reactions: special chlorophyll a molecule transfers its excited e- to the primary e- acceptor

7. A Photosystem : A Reaction Center Associated with Light-Harvesting Complexes A photosystem Is composed of a reaction center surrounded by a number of light-harvesting complexes Primary election acceptor Photon Thylakoid Light-harvesting complexes Reaction center Photosystem STROMA Thylakoid membrane Transfer of energy Special chlorophyll a molecules Pigment molecules THYLAKOID SPACE (INTERIOR OF THYLAKOID) e –

8. Light-harvesting Complexes and Reaction Centers The light-harvesting complexes consist of pigment molecules bound to particular protein They funnel the energy from photons of light to the reaction center When a reaction-center chlorophyll a molecule absorbs energy, one of its electrons gets bumped up to a primary electron acceptor

9. Two types of photosystems embedded in the thylakoid membranes of land plants (fig 10.13) 1. Photosystem I ( PS I ) Rxn center chlorophyll a = P700 Cyclic and noncyclic e- flow 2. Photosystem II ( PS II ) Rxn center chlorophyll a = P680 Noncyclic e- flow Noncyclic e- flow (fig 10.13) Uses PS II & PS I Excited e- from PS II  goes through ETC  produces ATP Excited e- from PS I  ETC  used to reduce NADP+ Electrons ultimately supplied from splitting water  releases O 2 and H + Cyclic e- flow (fig 10.15) Uses only PS I Only generates ATP Excited e- from PS I cycle back from 1st ETC No O 2 release & no NADPH made Photosystems

10. Two Photosystems The thylakoid membrane Is populated by two types of photosystem I and II.

11. Noncyclic Electron Flow – Involves both Photosystems Produces NADPH, ATP, and oxygen, and is the primary pathway of energy transformation in the light rxns. Figure 10.13 Photosystem II (PS II) Photosystem-I (PS I) ATP NADPH NADP + ADP CALVIN CYCLE CO 2 H 2 O O 2 [CH 2 O] (sugar) LIGHT REACTIONS Light Primary acceptor Pq Cytochrome complex PC e P680 e – e – O 2 + H 2 O 2 H + Light ATP Primary acceptor Fd e e – NADP + reductase Electron Transport chain Electron transport chain P700 Light NADPH NADP + + 2 H + + H + 1 5 7 2 3 4 6 8

12. Cyclic Electron Flow; Under certain conditions Photoexcited electrons take an alternative path Uses Photosystem I only

13. In cyclic electron flow In cyclic electron flow Electrons cycle back to the first ETC Only ATP is produced Primary acceptor Pq Fd Cytochrome complex Pc Primary acceptor Fd NADP + reductase NADPH ATP Figure 10.15 Photosystem II Photosystem I NADP +

14. Primary electron acceptor Primary electron acceptor Electron transport chain Electron transport Photons PHOTOSYSTEM I PHOTOSYSTEM II Energy for synthesis of by chemiosmosis Noncyclic Photophosphorylation Photosystem II regains electrons by splitting water, leaving O 2 gas as a by-product

15. Plants produce O 2 gas by splitting H 2 O The O 2 liberated by photosynthesis is made from the oxygen in water (H + and e - )

16. 2 H  + 1 / 2 Water-splitting photosystem Reaction- center chlorophyll Light Primary electron acceptor Energy to make Electron transport chain Primary electron acceptor Primary electron acceptor NADPH-producing photosystem Light NADP  1 2 3 How the Light Reactions Generate ATP and NADPH

17. Summary—Light Dependent Reactions a. Overall input light energy, H 2 O. b. Overall output ATP, NADPH, O 2 .