Lecture 12 - 013111

Lecture 12 - 013111 - Lecture 12 The Calvin Cycle 1 Calvin...

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1 Lecture 12 The Calvin Cycle
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2 Calvin Cycle — Dark reactions (light- independent) The Whole Purpose: Use ATP and NADPH to reduce CO 2 Glyceraldehyde- 3-phosphate Where did ATP and NADPH come from?
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3 Calvin Cycle: three stages 1. Fixation of CO 2 2. Reduction of 3- phospoglycerate to form hexose sugars 3. Regeneration of 1,5- bisphosphate
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4 Stage 1: Fixation Condensation hydrolysis D ’ = -35.1 kJ mol -1 Driven by splitting into the two 3C’s Not in animals Here is where the CO 2 is added 5C 2x 3C
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Stage 1: Fixation Radioactivity of 14 CO 2 is traced • within 5s, incorporation of CO 2 into 3-phosphoglycerate shown in irradiated cultures of algae. •Within 60s, incorporation of CO 2 into many compounds Intermediate compounds in the Calvin cycle 5
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Catalyzed by RuBisCo : greatest amount of total protein of any kind on Earth Ribulose 1,5-bisphosphate carboxylase/oxygenase Located on the stromal surface of the thylakoid membranes Rate limiting step in hexose synthesis 8 large (L) (catalytic + regulation sites) and 8 small (S) subunits Most abundant Slow enzyme 6
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Catalyzed by RuBisCo : mechanism Non-substrate CO 2 7 •A metal ion (Mg 2+ ) activates a bound substrate by stabilizing a negative charge •A carbamate is needed for the metal ion binding •Carbamate formation is facilitated by the enzyme RuBisCo activase
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9 Catalyzed by RuBisCo : mechanism Hydrolysis by adding H 2 O to the β-ketoacid
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Lecture 12 - 013111 - Lecture 12 The Calvin Cycle 1 Calvin...

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