Lecture 101. Explain how photosynthesis relates to the electron towera. Light enrgy excites a weak e- donor into a strong e- donor which passes e- downthe electron tower2. Recall the two steps in photosynthesis a. ATP productionb. CO2 reduction to cell material (CO2 fixation)3. Explain why photosynthesis always involves membranes a. Because it occurs in chlorophylls which have 2 membranesb. PMF is used to generate ATP H+ extruded outside of membrane4. Explain how ATP is produced in photosynthesis a. When the excited electron donor passes e- down the chain, H+ is extruded to produce ATP5. Recall the stoichiometry of the Calvin cyclea. 6CO2 + 12NADH + 18ATP = Fructose-6P + 12 NADP+ + 18 ADP + 18Pi 6. Compare and contrast the different bacterial phototrophs (which photosynthetic pathways and which CO2 fixation mechanisms) a. Cyanobacteriai. Perform oxygenic photosynthesis ancestors of chloroplasts, contain thylakoid membranesb. Purple bacteriai. Anoxygenic photosynthesis- does not produce oxygenii. Purple sulfur bacteria: often sulfur granules in the periplasmiii. Purple non-sulfur bacteriac. Green bacteriai. Anoxygenic photosynthesis contain chlorosomesii. Green sulfur bacteria: often sulfur granules outside or attached to the celliii. Green no sulfur bacteriad. Heliobacteriai. Anoxygenic photosynthesisii. Photoheterotrophsiii. Need organic carbon for growthiv. Do not fix CO27. Explain why all photosynthesis pigments are membrane-bound a. Light harvesting is the transfer of energy by chlorophylls and phycobiliproteins to the reaction center where electron transport beginsb. Must be lipid soluble (long hydrocarbon chains)8. Explain the function of carotenoids a. Present in all photosynthestic organismsb. Function in photoprotection, can also increase efficiency of light harvestingc. Alternating double bonds of long hydrocarbon chainsd. Membrane bounde. Many colorsf. Large variety in bacteria9. Explain the function of phycobiliproteins a. Phycobilins attached to proteinsb. In bacteria exist only in cyanobacteriac. Function in light harvestingd. Phycobiliproteins form large light harvesting complexes (phycobilisomes)e. Non toxic non carcinogenic dyes10. Explain the function of chlorophylls a. Vareity of cholorphylls and bacteriochlorophyllsb. Different chlorophylls absorb different lightsc. Located in the reaction centers of photosynthetic membranesd. Less competition for light energy11. Compare and contrast different chlorophylls and bacteriochlorophylls a. Chlorophyll is associated with oxygenic photosynthesisb. Bacteriochlorophylls are associated with anoxygenic photosynthesis12. Explain cyclic photophosphorylation a. PSI absorbs a photon and transfer the e- to ferrodoxin. Instead oftransferring e- to ferrodoxin-NADH reductase, the e- are transferred to plastoquinone, which goes through the cytochrome bf complex and through plastocyanin and eventuallyback to p700. Cyclic photophosphorylation generates a proton gradient to make ATP, but does not generate NADPH.13. Compare and contrast photosynthesis and respiration (from lecture 9) 14. Explain why oxygenic photosynthesis is called the Z scheme a. Electron gets excited, travels down ekectron tower throught PSII, then gets excited and travels fown again through PSI15. Compare and contrast photosystems I and II in oxygenic photosynthesis a. PSIi. Chlorophyll P700; potential less positive than O2/H2O ii. P700* is a strong electron donoriii. e- transport produces PMF or NAD(P)H iv. Electrons used to make NAD(P)H are replaced by PSIIb. PSIIi. Chlorophyll P680, potential more positive than O2/H2O ii. Electrons are transported through a non-cyclic electron transport chain to photosystem I, creating a PMF iii. P680* gives electron16. Explain why the electron flow is called non-cyclic in oxygenic photosynthesis a. After Cyt bf, plastocyanin (PC) donates the electrons to PSI, instead of the electron going back to the beginning of PSII17. Compare and contrast oxygenic and anoxygenic photosynthesisa. Oxygenici. Uses water as a source of electrons for energy production yielding O2 as a productb. Anoxygenici. Uses other sources of reduced chemicals for electrons18. Compare and contrast oxygenic photosynthesis and oxygen respiration a. Respirationi. Don’t need sunlightii. Oxygen is absorbed and carbon dioxide is released.iii. Breakdown of foodb. Photosynthesisi. Need sunlight ii. Carbon dioxide is absorbed and oxygen is released.iii. Production of
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