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) Photosystems: PS I [P 700 ] and PS II [P 680 ]

Noncyclic Photophosphorylation Process of making ATP from ADP + P i using energy derived from light 7 steps: 1)Photosystem II 2)Primary electron acceptor 3)Electron transport chain 4)Phosphorylation 5)Photosystem I 6)NADPH 7)Photolysis

Noncyclic Photophosphorylation Summary –Takes light energy and electrons from H 2 O to make the energy-rich molecules ATP and NADPH –Light-dependent reactions, or light reactions

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

Calvin-Benson Cycle (Dark Reactions) Fixes CO 2 Takes inorganic CO 2 and incorporates it into an organic molecule that can be used in biological systems Goal: produce a single molecule of glucose (C 6 H 12 O 6 ) Must repeat 6 times, using 6 CO 2 molecules

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

Calvin-Benson Cycle (Dark Reactions) Summary –6CO ATP + 12 NADPH  18 ADP + 18 P i + 12 NADP glucose

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

Chemiosmotic Theory Describes the mechanism by which ADP is phosphorylated to ATP Steps: 1)H+ ions (protons) accumulate inside the thylakoids 2)A pH and electrical gradient (electrochemical) across the thylakoid membrane is created 3)ATP synthase generate ATP

Photorespiration Ribisco has the ability to fix O 2, as well as carbon dioxide Problems: –Decrease efficiency of CO 2 fixation –Products formed react with RuBP do not lead to useful, energy-rich molecules Peroxisomes breakdown these products

C 4 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

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)