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Biochemistry

Biochemistry. Lecture 15. Photosynthesis. Chemiosmotic Gradient. Endosymbiotic Theory. Photosynthesis. Assimilation of CO 2 by Plants. CO 2 Assimilation Occurs in Plastids. Organelles found in plants and algae Enclosed by a double membrane Have their own small genome

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Biochemistry

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  1. Biochemistry Lecture 15

  2. Photosynthesis

  3. Chemiosmotic Gradient

  4. Endosymbiotic Theory

  5. Photosynthesis

  6. Assimilation of CO2 by Plants

  7. CO2 Assimilation Occurs in Plastids Organelles found in plants and algae Enclosed by a double membrane Have their own small genome The inner membrane is impermeable to ions such as H+, and to polar and charged molecules

  8. Origin and Differentiation of Plastids Plastids were acquired during evolution by early eukaryotes via endosymbiosis of photosynthetic cyanobacteria Plastids reproduce asexually via binary fission The undifferentiated protoplastids in plants can differentiate into several types, each with a distinct function Chloroplasts for photosynthesis Amyloplasts for starch storage Chromoplasts for pigment storage Elaioplasts for lipid storage Proteinoplasts for protein storage

  9. Photosynthesis

  10. Review: Light Reactions Generate ATP and NADPH

  11. The Calvin Cycle

  12. Rubisco (ribulose 1,5 bisphosphate carboxylase / oxygenase )

  13. The Calvin Cycle

  14. Rubisco is Activated via Covalent Modification of the Active Site Lysine

  15. Fates of G3P

  16. Remaking R1,5BP

  17. Photorespiration So far, we saw that plants oxidize water to O2 and reduce CO2 to carbohydrates during the photosynthesis Plants also have mitochondria where usual respiration with consumption of O2 occurs in the dark In addition, a wasteful side reaction catalyzed by Rubisco occurs in mitochondria This reaction consumes oxygen and is called photorespiration; unlike mitochondrial respiration, this process does not yield energy

  18. Oxygenase Activity of Rubisco The reactive nucleophile in the Rubisco reaction is the electron-rich enediol form of ribulose 1,5-bisphosphate The active site meant for CO2also accommodates O2 Mg++ also stabilizes the hydroperoxy anion that forms by electron transfer from the enediol to oxygen

  19. Salvage of 2-Phosphoglycerate Complex ATP-consuming process for the recovery of C2 fragments from the photorespiration Requires oxidation of glycolate with molecular oxygen in peroxisomes, and formation of H2O2 Involves a loss of a carbon as CO2 by mitochondrial decarboxylation of glycine

  20. Rubisco in C3 Plants Cannot Avoid Oxygen Plants that assimilate dissolved CO2 in themesophyll of the leaf into three-carbon 3-phosphoglycerate are called the C3 plants Our atmosphere contains about 21% of oxygen and 0.038% of carbon dioxide The dissolved concentrations in pure water are about 260 M O2 and 11 M CO2(at the equilibrium and room temperature) The Km of Rubisco for oxygen is about 350 M

  21. Separation of CO2 capture and the Rubisco Reaction in C4 Plants Many tropical plants avoid wasteful photorespiration by a physical separation of CO2 capture and Rubisco activity CO2 is captured into oxaloacetate (C4) in mesophyll cells CO2 is transported to bundle-sheath cells where Rubisco is located The local concentration of CO2 in bundle-sheath cells is much higher than the concentration of O2

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