Cellular Respiration + Fermentation

If there are sufficient amounts of ATP, phosphofructokinase, the enzyme that catalyzes the third step of glycolysis, is inhibited. Thus, cellular respiration occurs at a slower rate. However, if cells are not producing sufficient amounts of ATP, phosphofructokinase is stimulated, thus speeding up the rate of cellular respiration.

In glycolysis, the enzyme phosphofructokinase converts fructose-6-phosphate into fructose-1,6-bisphosphate. Now, you know how ATP is made in respiration? ATP is an allosteric inhibitor of that enzyme. If the enzyme is inhibited, glycolysis stops functioning, and no more ATP is produced. You have to remember that the cell is very efficient. Why make more than necessary when those resources could be spent elsewhere?

Conversely, the molecule AMP (adenosine monophosphate) is an allosteric activator of the same enzyme. An abundance of AMP means that not enough ATP is in the cell, so activation of the enzyme will expedite glycolysis and thus ATP synthesis.

Additionally, in the citric acid cycle, the first intermediate, citrate, is an inhibitor for phosphofructokinase as well. If citrate accumulates, some is passed out of the mitochondrial matrix into the intermembrane space, inhibiting glycolysis once again.


Both occur anaerobically. Lactic acid fermentation would occur in muscle and ethanol fermentation would occur by yeast. The end products are different of course as one produces lactic acid and the other ethanol.

Two questions per thread.