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Photophosphorylation

Photophosphorylation. Light-driven proton pump : no CO 2 fixed; source of energy to generate PMF Anoxygenic photosynthesis : No O 2 generated; CO 2 fixation Oxygenic photosynthesis : O 2 generated; CO 2 fixation. Pigment Abs (nm). a 805, 830-890. Purple bacteria.

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Photophosphorylation

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  1. Photophosphorylation • Light-driven proton pump : no CO2 fixed; source of energy to generate PMF • Anoxygenic photosynthesis : No O2 generated; CO2 fixation • Oxygenic photosynthesis : O2 generated; CO2 fixation

  2. Pigment Abs (nm) a 805, 830-890 Purple bacteria b 835-850, 1020-1040 c 745-755 d 705-740 Green sulfur bacteria e 719-726 Why absorb at different wavelengths?

  3. absorb different wavelengths of light than chlorophylls Figure 9.27

  4. Reverse electron flow more positive E0 more negative E0 Figure 9.32 ATP or PMF used to drive “upward” (reverse) flow of electrons

  5. Sulfur granules deposited outside Sulfur granules deposited inside

  6. electron flow  PMF  ATP Figure 9.30

  7. Anabolic principles • Energy from catabolism  anabolism • Complex macromolecules composed of limited number of monomers (20 aa) • Redundancy of enzymes, not pathways • Compartmentalization • Self-assembly of macromolecular complexes, ex. ribosomes

  8. Methods • Cell-free extracts • Biochemically identify enzymes and intermediates • Nutritional mutants and cross-feeding • Radioactive intermediates and precursors

  9. Identification of anabolic pathways E1 E2 E3 A B C Z

  10. Photosynthesis • Light reactions: • Light energy harvested to generate energy • Dark reactions: • Energy used to fix CO2 • Calvin Cycle

  11. Uridine diphosphate glucose (UDPG) and the synthesis of sugars Figure 10.6 Figure 10.7

  12. Recall - Assimilation of: • Phosphorus • Sulfur • Nitrogen • CO2 fixation and anapleurotic reactions • Details found in Chapter 10 of text

  13. Anaplerotic Reactions • replenish TCA cycle intermediates • allow TCA cycle to function during periods of active biosynthesis • e.g., anaplerotic CO2 fixation • e.g., glyoxylate cycle

  14. Anaplerotic CO2 fixation pyruvate carboxylase: pyruvate + CO2 oxaloacetate phosphoenol- pyruvate (PEP) carboxylase: PEP + CO2 oxaloacetate Figure 10.17

  15. Glyoxalate cycle a modified TCA cycle Figure 10.20

  16. Amino acid biosynthesis

  17. Nucleotide synthesis • Purines • cyclic nitrogenous bases consisting of 2 joined rings • adenine and guanine • Pyrimidines • cyclic nitrogenous bases consisting of single ring • uracil, cytosine, and thymine • Nucleoside = nitrogenase base-pentose sugar • Nucleotide = nucleoside-phosphate

  18. initial products are ribonucleotides deoxyribonucleotides formed by reduction of nucleoside diphosphates or nucleoside triphosphates

  19. ribonucleotides are initial products deoxy forms of U and C nucleotides formed by reduction of ribose to deoxyribose

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