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Exam Review - Chapter 20

Pep carboxylase fixes co2 in the form of malate the

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Unformatted text preview: cell o Salvaging 2- phosphoglycolate requires cellular energy o Becomes a problem for plants because increase in temperature reduces rubisco’s affinity for CO2 o As CO2 is consume,d the ratio of O2 to CO2 increases, favoring the oxygenase reaction Glycolate Pathway: converts two molecules of 2- phosphoglycolate to a molecule of serine and a molecule of CO2 • Phosphatase converts 2- phosphoglycolate to glycolate, which is exported to peroxisome • Glycolate is oxidized by O2 and the resulting aldehyde undergoes transamination to glycine o Hydrogen peroxide is formed as a side product of glycolate oxidation and rendered harmless by peroxidases • Glycine goes from the peroxisome to the mitochondrial matrix, where it undergoes decarboxylation by the glycine decarboxylase complex o Oxidizs glycine to CO2 and NH3 with the reduction of NAD+ to NADH and the transfer of carbon to tetrahydrofolate o Carbon on tetrahydrofolate is then transferred to a second glycine by serine hydroxymethyltransferase, producing serine o Serine is eventually converted to 3- phosphoglycerate, used to regenerate ribulose 1,5- bisphosphate • Oxidative photosynthetic carbon cycle, C2 cycle: photorespiration C4 Plants • Temporary fixation of CO2 into a four- carbon compound oxaloacetate • Involves two types of cells : mesophyll cells and bundle sheath cells 1. HCO3- is fixed into oxaloacetate by phosphoenolpyruvate (PEP) carboxylase 2. Oxaloacetate formed is either reduced to malate or converted to aspartate a. Passes into neighboring bundle- sheath cells 3. Malate is oxidized and decarboxylated to yield pyruvate and CO2 by malic enzyme, reducing NADP+ 4. Aspartate is transaminated to form oxaloacetate and reduced malate a. The CO2 is released by malic enzyme or PEP carboxylase b. CO2 is f...
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