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Obligate anaerobes: Primitive bacteria (eg Clostridium) for them O2 is poisonous.
Facultative anaerobes: Yeasts (also muscle tissue) can withstand a lack of oxygen for short periods. Can also respire aerobically.
Anaerobic respiration is less efficient. The electron transport chain needs free oxygen to function. Only a few molecules of ATP are produced by reactions directly coupled to the oxidation of glucose in glycolysis.
Net ATP gain per molecule of glucose = 2ATP
But what is to be done with all the spare electrons and protons?
These are used to reduce:
Facultative anaerobes must control themselves:
Much more ATP is produced in the presence of O2 (18 times more)
ATP and Citrate (formed in the Kreb's Cycle) inhibit the enzyme that phosphorylates glucose (phosphofructokinase) at the beginning of glycolysis. This is known as the Pasteur effect, a good example of allosteric inhibition.
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