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Central metabolism Where do the molecules we eat come from? polysaccharides glucose glycolysis fermentation organic wastes ATP proteins lipids acetyl CoA amino acids TCA cycle ATP ATP ATP oxidative phosphorylation CO2 ATP ATP Photosynthesis Ultimate source of carbon and energy for all living things Halobacterium: Simplest photosynthesis Bacteriorhodopsin uses light energy to pump protons light H+ outside cytoplasm H+ H+ H+ H+ H+ H+ H+ H+ bacteriorhodopsin H+ H+ H+ H+ H+ H+ H+ H+ H+ H+ ATP synthase ADP ATP Plants have been doing this for a while… Plant photosynthesis overview Light powers ATP synthesis CO2 + ATP used to synthesize glucose CO2 light energy glucose ATP Reactions of photosynthesis Light-dependent: capture energy as ATP and NADPH Light-independent: CO2 → glucose (“fix” carbon) CO2 light energy glucose ATP 6 CO2 + 6 H2O + Light Energy C6H12O6 + 6 O2 The chloroplast Light-dependent reactions in thylakoid membrane Light-independent reactions in stroma o.m. i.m. stroma t.m. thylakoid thylakoid space granum Light-dependent reactions Capture light energy as ATP and NADPH Occur in thylakoid membrane e- free energy (G) photosystem II light light ADP ATP e- e- photosystem I NADP NADPH e- Chlorophyll Light-harvesting pigment in thylakoid membrane Lipid-like structure with large carbon ring Absorbs blue and red wavelengths of light (reflects back green) Photosystem II “Satellite dish” of chlorophyll in membrane Light-gathering “antenna” molecules Pass energy to “reaction center” or (“special pair”) chlorophyll light Photosystem II Reaction center chlorophyll oxidizes H2O → O2 Using light energy, energizes e– Transfers e– to electron transport chain e- light e– H2O O2 electron carrier photosystem II light e- Photosystem II Electron transport Cytochrome oxidase complex pumps H+ into thylakoid space Electrons transferred to Photosystem I stroma H2O photosystem II H+ cytochrome oxidase complex O2 photosystem I e– thylakoid space H+ H+ H+ H+ H+ H+ Photosystem II H+ gradient used to synthesize ATP ATP stroma H2O photosystem II O2 ADP ATP synthase H+ cytochrome oxidase complex H+ e– thylakoid space H+ H+ H+ H+ H+ H+ H+ H+ H+ H+ H+ H+ Photosystem I Second chlorophyll complex Re-energizes “used” electron e- free energy (G) photosystem II light light ADP ATP e- e- photosystem I NADP NADPH e- Photosystem I Electron transport Electron transferred to NADP+ → NADPH Electrons transferred to Photosystem I stroma H2O photosystem II H+ cytochrome oxidase complex O2 photosystem I e– thylakoid space H+ H+ H+ H+ H+ H+ NADP+ NADPH Light-dependent reactions Capture light energy as ATP and NADPH Why does the plant want NADPH? e- free energy (G) photosystem II light light ADP ATP e- e- photosystem I NADP NADPH e- Light-independent (“dark”) reactions ATP NADPH CO2 glucose Why does the plant want to make glucose? Light-independent (“dark”) reactions CO2 reduced to make glucose Occurs in stroma Calvin cycle CO2 ATP NADPH 3C carbohydrate glucose Light-independent (“dark”) reactions Key reaction catalyzed by RuBisCo Ribulose bisphosphate carboxylase Most abundant enzyme! CO2 RuBisCo 5C 6C 3C 3C Photosynthesis CO2 light ADP ATP NADP NADPH H+ H2O O2 glucose Which organelle would not be found in a plant cell? a. Chloroplast b. ER c. Mitochondrion d. Golgi e. Nucleus f. none of the above light glucose ATP Respiration & photosynthesis: similarities Harvest energy in usable forms Electron transport Multi-step biochemical pathway Oxidation-reduction O2