So metabolites such as pyruvate molecules or ATP molecules or citrate molecules actually depend on special protein transporters to move across the two sides of the membrane. Now, if we examine, if we take a small section of this region here, this is what we're going to get. So this is the outer and the inner membrane. Now, the inner membrane, on the matrix side, we have a negative charge. On the intermembrane space side, we have a positive charge. And that's why this side of the membrane is called the N side, n for negative, and this side is called the pside P for positive.