CATABOLISM
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CHEMOTROPHS |
PHOTOTROPHS |
" FERMENTATION:To make a long story short, we can use the example of a typical fermentation pathway (stepwise/sequential chain of chemical reactions) where glucose is oxidized to pyruvate (the oxidation stage of the pathway) and pyruvate is then reduced to fermentation products such as lactic acid (the reduction stage of the pathway). At a certain step in the oxidation stage where compound A loses electrons (which are picked up by co-enzyme NAD+), the electrons can be transferred to compound C in the reduction stage (thus "regenerating" the NAD+). In the generation of ATP, the "P" (phosphate) can be "free" (inorganic) or attached to an intermediate compound in the pathway (organic). As this phosphate is transferred to ADP in the formation of ATP and does not incorporate energy associated with electron transport, the term "substrate-level phosphorylation" applies. |
" PHOTOTROPHY:
Phototrophy can be OXYGENIC (evolving O2 when H2O serves as the electron donor) or ANOXYGENIC (non-O2-evolving). Note in these pages that cyclic vs. non-cyclic photophosphorylation is not (yet) addressed. |
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" RESPIRATION: |
While fermenters tend to be organotrophs, respirers can be organotrophs or lithotrophs. For respiration, we have O2 as an external electron acceptor, and the reduction stage seen in fermentation is replaced here by continued oxidation. An organic substrate can be oxidized completely to CO2 as O2 is reduced to H2O. ANAEROBIC RESPIRATION employs an electron acceptor other than O2 such as nitrate (NO3–) which is reduced to nitrite (NO2–) or N2. |
An attempt to produce an abbreviated summary of catabolism based on the above follows. The above basic flow diagram can be expanded to address the concept of "reducing power," the provision of electrons and ATP to anabolic activities, and the key role of NAD: Combining Terms: Using the terms describing organisms according to their source of energy and reducing power as defined above, one can combine these terms as follows: chemoorganotroph, chemolithotroph, photoorganotroph, and photolithotroph. Considering the terminology associated with the source of carbon as explained here, one finds that most chemoorganotrophs are chemoheterotrophs (and vice versa), and most chemolithotrophs are chemoautotrophs (and vice versa). With this in mind, the following terms are paired accordingly: photoorganotrophs with photoheterotrophs, and photolithotrophs with photoautotrophs. Reasons why an organism may grow anaerobically are summarized here. |
A page on the Bact. 102 website summarizing catabolism and the test for oxygen relationships can be found here. |
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Selected General Microbiology Topics: " Bacterial Nutrition and Growth " Review of the Cycles of Elements " Differential Media Site Archived Bacteriology 102 Site Site Outline of related pages |
These general microbiology pages have copyright by John Lindquist |