Lecture33-2009-Li

Lecture33-2009-Li - Photosynthesis II Lecture 33 Chapter...

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Photosynthesis II Lecture 33 Chapter 19-3
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Summary • CO 2 Fixation - role of Ribulose Bisphosphate Carboxylase (RuBisCO) Rest of the Calvin Cycle (Carbon Reactions) pathway Photorespiration Regulation of Calvin Cycle
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Figure 19-11 “Light reactions” of photosynthesis produce large amounts of NADPH and ATP in the Stroma
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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. – Fixing of CO 2 occurs in the stroma: Calvin Cycle (after Melvin Calvin). Gluconeogenesis: synthesis of glucose from non-carbohydrate precursors, but not CO 2 . Animals cannot fix carbon. Heterotrophs (other feeders). Plants are autotrophs (self feeders).
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Melvin Calvin experiment: Nobel Prize for Chemistry (1961) Using C-14 isotope tracer, mapped C route through a plant during photosynthesis Light acts on Chlorophyll, rather than CO 2 Radioactive 3- phosphoglycerate formed within 5 seconds of adding
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Figure 19-26 Calvin Cycle: Substrates: ATP NADPH CO 2 Product: GAP Stage 1 Production Stage 2 Recovery 2 +
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1 2 3 4 kinase kinase DeH
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Reaction 1: Phosphoribulose kinase (Mg ++ ) Ru5P + ATP --> RuBP + ADP
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Reaction 2: Ribulose-1,5- bisphosphate carboxylase- oxygenase RuBisCO or RuBP carboxylase
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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 biosphere.
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Eight large (L) and eight small (S) subunits. L contains active site. Not clear what S does (regulatory?). RuBP analog in active site
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This note was uploaded on 11/26/2009 for the course BIO 361 taught by Professor Lake during the Fall '08 term at SUNY Stony Brook.

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Lecture33-2009-Li - Photosynthesis II Lecture 33 Chapter...

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