Lecture30-2007 - "Light reactions" of...

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1 Photosynthesis II Lecture 30 Chapter 18-3 “Light reactions” of photosynthesis produce large amounts of NADPH and ATP in the Stroma What to do with ATP and NADPH? • Use to “fix” carbon: – Use ATP and NADPH to polymerize CO 2 (lowest energy form of C) into glucose. • Gluconeogenesis: synthesis of glucose from non-carbohydrate precursors, but not CO 2 . • Animals cannot fix carbon. Heterotrophs (other feeders). • Plants are autotrophs (self feeders). • Fixing of CO 2 occurs in the stroma: Calvin Cycle (after Melvin Calvin). Melvin Calvin experiment: Radioactive 3- phosphoglycerate formed within 5 seconds of adding 14 CO 2 to algae in presence of light. Further incubation (1 minute) results in many products.
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Calvin Cycle: Substrates: ATP NADPH CO 2 Product: GAP Stage 1 Production Stage 2 Recovery Overall: 3 CO 2 + 9 ATP + 6 NADPH --> GAP + 9 ADP + 8 Pi + 6 NADP + Reaction 1: Phosphoribulose kinase (Mg ++ ) Ru5P + ATP --> RuBP + ADP Reaction 2: Ribulose-1,5- bisphosphate carboxylase- oxygenase RuBisCO or RuBP carboxylase RuBisCO • Balanced equation: CO 2 + RuBP + H 2 O --> 2 3-phosphoglycerate • Highly favorable reaction: ! G o’ = -35.1 kJ/mole • Requires Mg 2+ • Very slow: 3/sec • Most abundant protein in biosphere (up to 50% of leaf protein). • Arguably most important enzyme in
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Lecture30-2007 - "Light reactions" of...

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