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Photosynthesis

Photosynthesis. The process of converting energy from sunlight to energy in chemical bonds. 6CO 2 + 6H 2 O + light  C 6 H 12 O 6 + 6O 2 Light absorbing pigments: Chlorophyll a (P 680 and P 700 ) Chlorophyll b Carotenoids (red, orange, or yellow)

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Photosynthesis

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  1. Photosynthesis • The process of converting energy from sunlight to energy in chemical bonds. • 6CO2 + 6H2O + light  C6H12O6 + 6O2 • Light absorbing pigments: • Chlorophyll a (P680 and P700) • Chlorophyll b • Carotenoids (red, orange, or yellow) • Photosystems: PS I [P700 ] and PS II [P680 ]

  2. Noncyclic Photophosphorylation • Process of making ATP from ADP + Pi using energy derived from light • 7 steps: • Photosystem II • Primary electron acceptor • Electron transport chain • Phosphorylation • Photosystem I • NADPH • Photolysis

  3. Noncyclic Photophosphorylation • Summary • Takes light energy and electrons from H2O to make the energy-rich molecules ATP and NADPH • Light-dependent reactions, or light reactions

  4. Cyclic Photophosphorylation • Electrons from PS I are “recycled” • Electrons from PS I join with the Electron Transport Chain and generate ATP, returning to PS I

  5. Calvin-Benson Cycle(Dark Reactions) • Fixes CO2 • Takes inorganic CO2 and incorporates it into an organic molecule that can be used in biological systems • Goal: produce a single molecule of glucose (C6H12O6) • Must repeat 6 times, using 6 CO2 molecules

  6. Calvin-Benson Cycle(Dark Reactions) • Carboxylation: 6 CO2 combine with Ru BP to produce 12 PGA • Enzyme: RuBP carboxylase, or Ribisco • Catalysis the rxn CO2 and RuBP (ribulose biphosphate) • Reduction: 12 ATP and 12 NADPH are used to convert 12 PGA to 12 PGAL • Regeneration: 6 ATP are used to convert 10 PGAL to 6 RuBP • Carbohydrate synthesis

  7. Calvin-Benson Cycle(Dark Reactions) • Summary • 6CO2 + 18 ATP + 12 NADPH  18 ADP + 18 Pi + 12 NADP+ + 1 glucose

  8. Chloroplast • Structure • Outer membrane • Inner membrane • Stroma • Enzymes for the Dark Rxns • Thylakoid • Contain the light-absorbing pigments and enzymes for the light rxns • Thylakoid compartment • Granum

  9. Chemiosmotic Theory • Describes the mechanism by which ADP is phosphorylated to ATP • Steps: • H+ ions (protons) accumulate inside the thylakoids • A pH and electrical gradient (electrochemical) across the thylakoid membrane is created • ATP synthase generate ATP

  10. Photorespiration • Ribisco has the ability to fix O2, as well as carbon dioxide • Problems: • Decrease efficiency of CO2 fixation • Products formed react with RuBP do not lead to useful, energy-rich molecules • Peroxisomes breakdown these products

  11. C4 Photosynthesis • PEP (phosphoenolpyruvate) • OAA (oxaloacetate) • PEP carbooxylase • Malate • Bundle sheath cells • Stomata are partially open during the day • Plants found in hot, dry climates • Sugar cane and crab grasses

  12. CAM Photosynthesis • PEP carboxylase • OAA • Malic acid • Stomata are closed during the day and OPEN at night • Vacuole • Plants found in hot, dry climates with cool nights (deserts)

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