Now, because the citric acid cycle is so important, we actually have to regulate this citric acid cycle. We have to closely monitor its activity, in fact, even before the citric acid cycle actually begins. One point of regulation of the citric acid cycle is by regulating Pyruvate decarboxylation because remember, Pyruvate decarboxylation must take place before the citric acid cycle actually begins. So in the cytoplasm of our cells, the glucose is transformed into Pyruvate via glycolysis. And under certain circumstances, the Pyruvate can even be transformed back into glucose. Now, if we have plenty of oxygen in our cell and our cell wants to produce ATP molecules, the Pyruvate will enter the matrix of the mitochondria.