So once glucose undergoes glycolysis in the cytoplasm and produces the pyruvate molecules in the presence of oxygen, those pyruvate molecules will migrate into the matrix of the mitochondria and they will move across the membranes of the mitochondria via special type of membrane protein we call pyruvate translocase. Now, what will happen to that pyruvate as soon as it moves moves into the matrix of the mitochondria? Well, it will not actually enter that citric acid cycle. Before it can enter the citric acid cycle, the pyruvate molecule must be prepared for that citric acid cycle. It must be activated. And that's why a process known as pyruvate decarboxylation actually takes place, pyruvate carboxylation, which is catalyzed by a large protein complex known as pyruvate dehydrogenase complex.