Electron transport system in chloroplast

Electron transport system in chloroplast

1. ELECTRON TRANSPORT SYSTEM IN CHLOROPLAST ANSHI RAHMAN AND Dr. KAYEEN VADAKKAN DEPARTMENT OF BIOTECHNOLOGY ST.MARY’S COLLEGE, THRISSUR

2. ETC is a series of complexes that transfer electrons from electron donors to electron accepters via redox reactions ,and couples the electron transfer with proton transfer across the membrane . This creates an electrochemical proton gradient that drives the synthesis of ATP . ELECTRON TRANSPORT SYSTEM IN CHLOROPLAST, NAME, ST.MAR’YS COLLEGE - THRISSUR

3. ELECTRON TRANSPORT SYSTEM IN CHLOROPLAST, NAME, ST.MAR’YS COLLEGE - THRISSUR

4. Photosynthesis, like respiration, is a redox (oxidation-reduction) process Water molecules are split apart by oxidation, which means that they lose electrons along with hydrogen ions (H + ) Then CO 2 is reduced to sugar as electrons and hydrogen ions are added to it ELECTRON TRANSPORT SYSTEM IN CHLOROPLAST, NAME, ST.MAR’YS COLLEGE - THRISSUR

5. PHOTOSYNTHESIS Light reaction Dark reaction Light reaction of photosynthesis are those directly depend on the absorption of light the resulting photochemistry takes electrons from H2O and drives them through a series of membrane bound carriers producing NADPH and NAD ELECTRON TRANSPORT SYSTEM IN CHLOROPLAST, NAME, ST.MAR’YS COLLEGE - THRISSUR

6. In photosynthesis, electrons gain energy by being boosted up an energy hill Light energy captured by chlorophyll molecules provides the boost for the electrons As a result, light energy is converted to chemical energy, which is stored in the chemical bonds of sugar molecules ELECTRON TRANSPORT SYSTEM IN CHLOROPLAST, NAME, ST.MAR’YS COLLEGE - THRISSUR

7. CHLOROPLAST This photosynthetic organelle contains three distinct membranes (the outer membrane, the inner membrane, and the thylakoid membrane) that define three separate internal compartments (the intermembrane space, the stroma, and the thylakoid. ELECTRON TRANSPORT SYSTEM IN CHLOROPLAST, NAME, ST.MAR’YS COLLEGE - THRISSUR

8. ELECTRON TRANSPORT SYSTEM IN CHLOROPLAST, NAME, ST.MAR’YS COLLEGE - THRISSUR

9. Important light absorbing pigments in thylakoid membrane are Chlorophyll –greenpigments. Chloroplast always contain Chlorophyll a and Chlorophyll b Chlorophyll is always associated with specific binding proteins –LHC(Light Harvesting Complexes) Addition to Chlorophyll thylakoid membrane contains secondary light absorbing pigments or accessory pigments –carotenoids. The light absorbing pigments of thylakoid or bacterial membrane are arranged in functional arrays called photosystems. ELECTRON TRANSPORT SYSTEM IN CHLOROPLAST, NAME, ST.MAR’YS COLLEGE - THRISSUR

10. Light reaction has three stages : Photon excitation-Absorption of light photon whose energy is used to split water releasing electron . Electron transport- Harnessing the energy in electron to form an electrochemical gradient. Two types: Cyclic and Non cyclic Photophosphorylation(Chemiosmosis)-ATP synthesis due to electro chemical gradient and proton motive force ELECTRON TRANSPORT SYSTEM IN CHLOROPLAST, NAME, ST.MAR’YS COLLEGE - THRISSUR

11. PHOTOSYSTEM Consist of a few hundred pigment molecules. Reaction centre contain Chlorophyll a that is next to a primary electron accepter Two types of photosystems have been identified and are called photosystem I and photosystem II Each type of photosystem has a characteristic reaction center Photosystem II, which functions first, is called P680 because its pigment absorbs light with a wavelength of 680 nm ELECTRON TRANSPORT SYSTEM IN CHLOROPLAST, NAME, ST.MAR’YS COLLEGE - THRISSUR

12. Numbers indicate optical wave length for absorption different absorption due to interaction with different portions in photosystems ELECTRON TRANSPORT SYSTEM IN CHLOROPLAST, NAME, ST.MAR’YS COLLEGE - THRISSUR Photosystem I, which functions next, is called P700 because it absorbs light with a wavelength of 700 nm.

13. ELECTRON TRANSPORT SYSTEM IN CHLOROPLAST, NAME, ST.MAR’YS COLLEGE - THRISSUR

14. TYPES OF ELECTRON TRANSPORT MECHANISMS Non-cyclic electron flow Cyclic electron flow ELECTRON TRANSPORT SYSTEM IN CHLOROPLAST, NAME, ST.MAR’YS COLLEGE - THRISSUR

15. ELECTRON TRANSPORT SYSTEM IN CHLOROPLAST, NAME, ST.MAR’YS COLLEGE - THRISSUR

16. N0N-CYCLIC ELECTRON FLOW PSll absorbs light Excited electron in reaction centre Chlorophyll (P680) captured by primary electron acceptor . P680 now losses an electron is a very strong oxidizing agent . Electrons are excited from water to replace the missing electronic P680 . As result , water is split into oxygen and hydrogen ions. ELECTRON TRANSPORT SYSTEM IN CHLOROPLAST, NAME, ST.MAR’YS COLLEGE - THRISSUR

17. ELECTRON TRANSPORT SYSTEM IN CHLOROPLAST, NAME, ST.MAR’YS COLLEGE - THRISSUR Electron captured by primary electron acceptor of PSll will now be passed through an electron chain. The electron is first transferred to pheophytin. Pheophytin very rapidly passes it’s extra electron to a protein bound plastoquinone,PQA.

18. Which in turns passes through another , more loosely bound plastoquinone PQB 4P680+4H+ +2PQB+4Photons . 4P680+ + 2PQH2 Pq is a mobile component within the thylakoid membrane . Electrons are transferred from Pq to Cytochrome complex . ELECTRON TRANSPORT SYSTEM IN CHLOROPLAST, NAME, ST.MAR’YS COLLEGE - THRISSUR

19. Protons across are pumped against its concentrateion gradient from step a across thylakoid membrane to the lumen. Electrons are transferred to plastoquinone (Pc). Pc is a movable component on lumen side of the thylakoid membrane . Electrons on P700 excited by light and captured by the primary electron acceptor leaving P700 oxidized. ELECTRON TRANSPORT SYSTEM IN CHLOROPLAST, NAME, ST.MAR’YS COLLEGE - THRISSUR

20. TOPIC, NAME, ST.MAR’YS COLLEGE - THRISSUR Electrons transferred from Pc to P700 replaces electrons that were lost. Electron undergo a second transport chain . First phylloquinone (A1)accepts electron and passes it to an iron sulphur protein

21. Electrons are transferred to ferredoxin (Fd). Fd is an iron containing mobile component on the strong side of the thylakoid membrane. Electrons transferred by enzyme NADP+ re ductase took the final electron acceptor NADP+. NADP+ is reduce to NADPH. ELECTRON TRANSPORT SYSTEM IN CHLOROPLAST, NAME, ST.MAR’YS COLLEGE - THRISSUR

22. ATP Synthase Protons pumped in to the lumen pass through –ATP synthase using the same mechanism as seen in cellular respiration . ATP is produced in the stroma. ELECTRON TRANSPORT SYSTEM IN CHLOROPLAST, NAME, ST.MAR’YS COLLEGE - THRISSUR

23. ELECTRON TRANSPORT SYSTEM IN CHLOROPLAST, NAME, ST.MAR’YS COLLEGE - THRISSUR

24. Summary Both PSl and PSll are involved H20 is split to produce O2 and H+ ions . Electron transport chain helps establish electrochemical proton gradient . Photophosphorylation:light –dependent formation of –ATP by Chemiosmosis . NADP+ is final electron acceptor and produces NADPH ELECTRON TRANSPORT SYSTEM IN CHLOROPLAST, NAME, ST.MAR’YS COLLEGE - THRISSUR

25. Cyclic electron transport Only involves photosysteml . Ferredoxin returns electrons back to cytochrome complex . Protons pumped into like to produce more ATP through Chemiosmosis . No NADPH produced ELECTRON TRANSPORT SYSTEM IN CHLOROPLAST, NAME, ST.MAR’YS COLLEGE - THRISSUR

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28. THANK YOU ELECTRON TRANSPORT SYSTEM IN CHLOROPLAST, NAME, ST.MAR’YS COLLEGE - THRISSUR

29. TOPIC, NAME, ST.MAR’YS COLLEGE - THRISSUR