Concluding Remarks

Photosynthesis is the process driven by the absorbance of light by chlorophyll and ending with the conversion of C02 into carbohydrate. Although there is a diversity among the photosynthetic organisms, there appears to be a great similarity in the process of photosynthetic electron transport and C02 fixation. Many reactions are employed to orchestrate the transfer of radiant energy to reduced carbon (chemical energy). The light reactions, which occur on thylakoid membranes (plants, algae, and cyanobacteria) and cell membranes (anoxygenic bacteria), begin with charge

Figure 6. The reductive pentose phosphate cycle. The RPP cycle contains 13 reactions (see Robinson and Walker [Ref. 12] for a description of the enzymes). The carboxylation and regeneration of three ribulose-l,5-bisphosphate (RuBP) molecules are shown. One extra C3 sugar is generated, which is either exported from the chloroplast or incorporated into starch. PGA: 3-phosphoglycerate; DPGA: 1,3-diphosphoglycerate; GAP: Glyceraldehyde-3-phosphate; DHAP: dihydroxyacetone phosphate; F-1,6-BP: fructose-l,6-bisphosphate; F-6-P: fructose-6-phosphate; X-5-P: xyulose-5-phos-phate; E-4-P: erythrose-4-phosphate; S-1,7-BP: sedoheptulose-l,7-bisphosphate; S-7-P: sedohep-tulose-7-phosphate; R-5-P: ribose-5-phosphate; G-l-P: glucose-1-phosphate.

Figure 6. The reductive pentose phosphate cycle. The RPP cycle contains 13 reactions (see Robinson and Walker [Ref. 12] for a description of the enzymes). The carboxylation and regeneration of three ribulose-l,5-bisphosphate (RuBP) molecules are shown. One extra C3 sugar is generated, which is either exported from the chloroplast or incorporated into starch. PGA: 3-phosphoglycerate; DPGA: 1,3-diphosphoglycerate; GAP: Glyceraldehyde-3-phosphate; DHAP: dihydroxyacetone phosphate; F-1,6-BP: fructose-l,6-bisphosphate; F-6-P: fructose-6-phosphate; X-5-P: xyulose-5-phos-phate; E-4-P: erythrose-4-phosphate; S-1,7-BP: sedoheptulose-l,7-bisphosphate; S-7-P: sedohep-tulose-7-phosphate; R-5-P: ribose-5-phosphate; G-l-P: glucose-1-phosphate.

separation in a reaction center and result in temporary storage of chemical energy as ATP and NADPH. This process alone requires the coordinated operation of pigmentprotein complexes, as well as numerous photochemical and redox reactions. The ATP and NADPH are then used in a complex, highly regulated metabolic cycle that fixes C02. Thus, photosynthesis entails a long chain of reactions, with each step playing an equally important role in sustaining life on our planet.

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