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Bacterial Physiology (Micr430)

Bacterial Physiology (Micr430). Lecture 4 Photosynthesis and Fermentation Pathways (Text Chapters: 5, 14). Photosynthesis. Definition: phototrophic or photosynthetic organisms – organisms that obtain most or all of their energy from light. Phototrophic Prokaryotes.

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Bacterial Physiology (Micr430)

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  1. Bacterial Physiology (Micr430) Lecture 4 Photosynthesis and Fermentation Pathways (Text Chapters: 5, 14)

  2. Photosynthesis • Definition: phototrophic or photosynthetic organisms – organisms that obtain most or all of their energy from light.

  3. Phototrophic Prokaryotes • Oxygenic phototrophs – most belong to cyanobacteria • Anoxygenic phototrophs • Purple photosynthetic bacteria • Purple sulfur bacteria • Purple non-sulfur bacteria • Green sulfur photosynthetic bacteria • Green non-sulfur photosynthetic bacteria • Heliobacterium

  4. Photosynthesis in Bacteria General scheme light Reaction Center Light harvesting pigments energy DE Bacteriochlorophyll is oxidized

  5. Photosynthetic Electron Transport • In purple photosynthetic bacteria Fig 5.1

  6. Reaction Center and ATP Synthase Fig 5.2

  7. Photosynthetic Electron Transport • In green photosynthetic bacteria Fig 5.5

  8. Photosynthetic Electron Transport • In cyanobacteria and chloroplasts Fig 5.7

  9. Photosynthetic Electron Transport • In cyanobacteria and chloroplasts • H2O is the electron donor, O2 is evolved • Two light reaction centers • Electron flow is primarily noncyclic, producing both ATP and NADPH

  10. Cyanobacteria vs Photosynthetic Bacteria • Cyanobacteria contain chlorophyll a, which is common to all eukaryotic algae and green plants. Water serves as the electron donor and oxygen is generated by photolysis • The purple bacteria contain bacteriochlorphyll a or b, while green bacteria contain bacteriochlorophyll c or d

  11. FERMENTATION PATHWAYS • A fermentation is defined as a pathway in which NADH is reoxidized by metabolites produced by the same pathway. • Characteristics: • Reactions usually occur in cytoplasm • ATP is produced via substrate-level phosphorylation • Occurs in the absence of oxygen • Most prevalent in prokaryotes

  12. Electron Sink • What to do with electrons generated during oxidation of compounds? • In aerobic organisms, electrons are transported to oxygen or nitrate during respiration • In fermentation, there is no exogenous electron acceptors; the fermentation pathway must produce its own electron acceptors (sinks) because they have to dispose of electrons generated during oxidation.

  13. Propionate Fermentation The Acrylate Pathway Fig 14.3

  14. Propionate Fermentation The Succinate-Propionate Pathway Fig 14.4

  15. Acetate Fermentation Fig 14.5

  16. Lactate Fermentation Homofermentative lactate fermentation

  17. Lactate Fermentation Heterofermentative lactate fermentation Fig 14.6

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