• If an isolated solution of chlorophyll is illuminated – It will fluoresce, giving off light and heat Excited state Energy of election Heat Photon (fluorescence) Chlorophyll molecule Ground state Photon e –
How do we capture the energy of that excited electron? ExcitedstateEnergy of electionHeatPhoton(fluorescence)ChlorophyllmoleculeGroundstatePhotone–
The Photosystem: The System of Organized Light Capture Components: A) Light Harvesting Complexes B) Reaction Center 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) Figure 10.12 e – Photosystem A reaction center surrounded by light-harvesting complexes How do we capture the energy of that excited electron?
The Photosystem A) Light-harvesting complexes (LH) – Consist of pigment molecules (chlorophyll a, chlorophyll b, carotenoids) bound to proteins – “Harvest light” and transfer the energy to the reaction center B) Reaction Center – 2 chlorophyll a molecules bound to proteins – Primary electron acceptor • Captures excited electron from LH complex, prevents it from plunging back to ground state
2 Types of Photosystems in Thylakoid Membrane • Photosystem I-discovered first • Photosystem II-discovered second LIGHT REACTOR NADP + ADP ATP NADPH CALVIN CYCLE [CH 2 O] (sugar) STROMA (Low H + concentration) Photosystem II LIGHT H 2 O CO 2 Cytochrome complex O 2 H 2 O O 2 1 1 ⁄ 2 2 Photosystem I Light THYLAKOID SPACE (High H + concentration) STROMA (Low H + concentration) Thylakoid membrane ATP synthase Pq Pc Fd NADP + reductase NADPH + H + NADP + + 2H + To Calvin cycle ADP P ATP 3 H + 2 H + +2 H + 2 H + Figure 10.17
How does the photosystem use the energy from the excited electrons? 2 Pathways: 1)Noncyclic Electron Flow -the primary pathway of energy transformation in the light reactions -Makes NADPH (electron carrier), ATP and O 2 2)Cyclic Electron Flow -makes ATP only
Non-Cyclic Electron Flow • Produces NADPH, ATP, and oxygen 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
Non-Cyclic Electron Flow • A mechanical analogy for the light reactions Mill makes ATP ATP e – e – e – e – e – Photon Photosystem II Photosystem I e – e – NADPH Photon Figure 10.14
Cyclic Electron Flow • In cyclic electron flow – Only photosystem I is used –
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