NEW lecture07 - Lecture 7: Friday May 21, 2010 Biology 172...

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Unformatted text preview: Lecture 7: Friday May 21, 2010 Biology 172 Todays Outline Announcements Photosynthesis- Overview- Light Reactions- Calvin Cycle Plants Unicellular protist Multicellular algae Cyanobacteria Purple sulfur bacteria 10 m 1.5 m 40 m Photoautotrophs: producers for most ecosystems Photoautotrophs Photosynthesis- the use of light energy to generate organic molecules Photosynthesis- the use of light energy to generate organic molecules- occurs in chloroplasts (plants/algae) or plasma membrane and cytosol (some proks) Chloroplasts Light microscope image Electron microscope image Chloroplasts Light microscope image Electron microscope image- possess 3 membranes Light microscope image Electron microscope image Stroma Lumen / Thylakoid Space (inside) Chloroplasts Light microscope image Electron microscope image- chlorophyll in thylakoid membrane absorbs light - possess 3 membranes Overview of Photosynthesis Two stages: Light Reactions Calvin Cycle Photo--synthesis Summary Reaction of Photosynthesis- basically the reverse of cellular respiration 6 CO 2 + 6 H 2 O + light C 6 H 12 O 6 + 6 O 2 Figure 10-1 Light energy Sunlight H 2 O O 2 Light-dependent reactions ATP , NADPH Chemical energy CO 2 Calvin cycle (CH 2 O) n Chemical energy H 2 O LIGHT REACTIONS Chloroplast Light ATP NADPH O 2 NADP + CO 2 ADP P + i CALVIN CYCLE [CH 2 O] (sugar) OUT: O 2 , sugar IN: light, water, CO 2 Todays Outline Photosynthesis- Overview Light Reactions Noncyclic Electron Flow Cyclic Electron Flow Calvin Cycle Summary of Photosynthesis Light Reactions of Photosynthesis causing electron to be boosted to a higher energy state (excited electron) First step: a photon of light is absorbed by a chlorophyll in a photosystem Like Figure 10.10 Photoexcitation of isolated chlorophyll Excited state E n e r g y o f e l e c t i o n e Heat Photon (fluorescence) Chlorophyll molecule Ground state Photon (a) Excitation of isolated chlorophyll molecule (b) Fluorescence Figure 10-11 Three Fates for Excited Electrons in Photosynthetic Pigments Reaction center Fluorescence Heat Photon Photon e e Electron acceptor Chlorophyll molecules in antenna complex Reaction center Chlorophyll molecule Lower Higher E n e r g y o f e l e c t r o n RESONANCE FLUORESCENCE REDUCTION/ OXIDATION or or e Electron drops back down to lower energy level; heat and fluorescence are emitted. Electron is transferred to a new compound. Energy in electron is transferred to nearby pigment. What happens to the high energy electrons transferred from Reaction Center? Figure 10-15 Noncyclic electron flow (Z-Scheme) during the light reactions links PSII and PSI , and generates ATP and NADPH 4e 4 Photons E n e r g y o f e l e c t r o n 2 H + 2 NADP + 2 NADPH Lower Higher Photosystem I Ferredoxin E T C + 4e 4 Photons E T C 4e Photosystem II 4 H + PQ PC P700 ATP produced via proton-motive force Cytochrome complex Pheophytin P680 + O 2 2 H 2 O How does Photosystem II (PSII) work? Figure 10-13...
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NEW lecture07 - Lecture 7: Friday May 21, 2010 Biology 172...

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