That is the intermembrane space. And we also have this region, which is the mitochondrial matrix. And the citric acid cycle, as well as pyruvate decarboxylation takes place in the mitochondrial matrix. So the electron transport chain itself consists of a series of four protein complexes. We have protein complex one, two, three and four. And we also have a complex of proteins shown here that is known as ATP synthase that actually uses the electrochemical gradient to synthesize ATP molecules.