Exam Review - Chapter 20

Oxygenase reaction results in no fixation of carbon

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Unformatted text preview: acetone phosphate is formed in the stroma and transported to the cytosol o converted to 3- phosphoglycearte and generates ATP and NADH Reductive assimilation of CO2 requires ATP and NADPH • several stromal enzymes have evolved to take advantage of light- induced contions, which signal the availability of ATP and NADPH o enzymes are more active in an alkaline environment and at high [Mg2+) • Certain enzymes are activated by light- driven reduction of disulfide bonds between two Cys residues that are critical to their activities o When these Cys residues are oxidized, they are inactive, normal when it is dark o With illumination, electrons flow from photosystem I to ferredoxin, which passes electrons to thioredoxin, which is catalyzed by ferredoxin- thioredoxin reductase o Thioredoxin donates electrons to the disulfide bonds of light- activated ezymes • At night, the Cys residues are reoxidized and inactivated 20.2: Photorespiration and the C4 and CAM Pathways • Photosynthetic cells produce O2 during the light- driven reactions and use CO2 during the light- independent processes • In the dark, plants carry out mitochondrial respiration, oxidation of substrates to CO2 and the conversion of O2 to H2O • Photorespiration: costly side reaction of photosynthesis • Rubisco is not absolutely specific for CO2 as a substrate O2 competes with CO2 at the active site o Rubisco can catalyze the condensation of O2 with ribulose 1,5- bisphosphate to form 3- phosphoglycerate and 2- phosphoglycolate, a useless product • The oxygenase reaction results in no fixation of carbon and is a net liability to the...
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This note was uploaded on 02/06/2014 for the course BCHB 501 taught by Professor Jessicajones,elliottcrooke,ericgalsgow,marybethmartin during the Fall '12 term at Georgetown.

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