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Photosynthesis: Introduction 6CO2 + 6H2O light CO2 O2 carbohydrate H2O C6H12O6 + 6O2 Photosynthesis is the initial source of energy for almost all biological activities Light ADP NADP+ C(H2O) O2 Heat NADPH ATP CO2 H2O Photosynthesis: plants, photosynthetic bacteria C(H2O) O2 CO2 H2O ADP NAD+ NADH ATP Respiration: plants, animals, bacteria, etc. Synthesis Movement Ion pumps Growth Reproduction Compare photosynthesis to respiration: Respiration: C6H12O6 + 6O2 6CO2 + 6H2O Go’ = -2840 kJ/mol Photosynthesis in green plants: 6 C O2 + 6H2O C6H12O6 + 6O2 Go’ = +2840 kJ/mol Unfavorable Go’ explains the need for energy input. That is the role of light. In higher plants, photosynthesis occurs in chloroplasts The aquatic plant, Elodea You may see dark grana inside some chloroplasts. Under an electron microscope, chloroplasts have a more complex structure. Chloroplast of Zea mays stroma grana lamellae stroma lamellae The concentration of grana varies among chloroplasts. Chloroplast of Pisum sativum Photosynthesis occurs in green plants, cyanobacteria, and some other bacteria Photosynthesis as described earlier: 6 C O2 + 6H2O C6H12O6 + 6O2 Compare photosynthesis in plants and bacteria Plants (divided by 6, H2O added to each side) CO2 + 2 H2O C(H2O) + O2 + H2O Green sulfur bacteria CO2 + 2 H2S C(H2O) + 2S + H2O Purple non-sulfur bacteria CO2 + 2 CH3CHOHCH3 isopropanol CO2 + 2 CH3CHOHCOOH lactate Generalize: CO2 + 2 H2D C(H2O) + 2 CH3COCH3 + H2O acetone C(H2O) + 2 CH3COCOOH + H2O pyruvate C(H2O) + 2 D + H2O D = H/electron donor Oxidation of D in H2D; reduction of C and O in CO2 How to measure photosynthesis Starch production 6CO2 + 6H2O C6H12O6 + 6O2 Van Helmont (1577-1644): A willow that grew for 5 years in a container gained more than a half centner in weight (ca 60 lbs), whereas the soil lost only 2 ounces. Illuminated leaves can be boiled in ethanol (to break membranes), then stained for starch with iodine. How to measure photosynthesis Starch production 6CO2 + 6H2O C6H12O6 + 6O2 Potato starch visualized by light microscopy… with a light iodine stain under polarized light How to measure photosynthesis O2 production 6CO2 + 6H2O C6H12O6 + 6O2 Priestly (1733-1804): Green plants give off oxygen and thus improve the air. Engelmann (1843-1909): produced the first action spectrum of photosynthesis using Spirogyra algae and aerotactic (oxygen-sensing) bacteria. How to measure photosynthesis CO2 uptake 6CO2 + 6H2O C6H12O6 + 6O2 Amoroso et al. Plant Physiol. 116:193 (1998) How to measure photosynthesis Dye bleaching (DCPIP reduction; Hill reaction) blue colorless (ZZZ = e- transport inhibitor) Light on Photosynthesis as described earlier: 6 C O2 + 6H2O C6H12O6 + 6O2 Compare photosynthesis in plants and bacteria Plants (divided by 6, H2O added to each side CO2 + 2 H2O C(H2O) + O2 + H2O Green sulfur bacteria CO2 + 2 H2S C(H2O) + 2S + H2O Purple non-sulfur bacteria CO2 + 2 CH3CHOHCH3 isopropanol CO2 + 2 CH3CHOHCOOH lactate Generalize: CO2 + 2 H2D C(H2O) + 2 CH3COCH3 + H2O acetone C(H2O) + 2 CH3COCOOH + H2O pyruvate C(H2O) + 2 D + H2O D = H/electron donor Oxidation of D in H2D; reduction of C and O in CO2 Oxidation of D in H2D; reduction of C and O in CO2 These reactions are separable. Dye bleaching, which occurs with O2 production, shows that the oxidation of H2O (or H2S, etc.) does not depend on the reduction of CO2 2 DCPIP (blue) + 2 H2O 2 DCPIPH2 (colorless) + O2 In the bacterial and plant photosynthetic reactions, CO2 + 2 H2D C(H2O) + 2 D + H2O The separate reactions are, 2 H2D light 2D 2 NADP+ 3 ADP + 3 Pi C(H2O) + H2O 2 NADPH + H+ 3 ATP (dark) CO2 . The light reactions produce H (reductant) and energy. Summary The reaction of photosynthesis can be summarized as: 6CO2 + 6H2O C6H12O6 + 6O2 or better, 6CO2 + 12H2O C6H12O6 + 6H2O + 6O2 But the product is starch, not C6H12O6 Photosynthesis can be measured as starch production, O2 production, CO2 uptake, or dye reduction The oxidation of H2O and the reduction of CO2 are separable If a sample of algae, when illuminated, releases 3 x 10-5 mol O2/min, how rapidly will it incorporate CO2? How much starch will be formed per minute? How many photons of light will be needed per minute?
