In the presence of oxygen, cells consume glucose. Within the inner membrane of each mitochondrion, the resulting molecules are processed through a series of reactions known as the Krebs cycle. The products of this cycle cause protons (H+) to diffuse through the inner membrane of the mitochondrion, from within the membrane out into the “matrix” (outer region) of the mitochondrion. As a result, a “chemiosmotic gradient”—similar to an electric potential—is produced. To relieve this gradient, the protons are allowed to drift back through the inner mitochondrial membrane.