The membrane of the mitochondria, made from a mosaic of proteins and lipids, is differentially permeable, allowing some compounds to pass through while preventing others from doing so. A change in the concentration of a chemical in the cytoplasm can cause a change in the mitochondrial membranes' permeability and, as a consequence, can affect the rate of chemical reaction in the mitochondria. Thus, factors that affect the permeability of a mitochondrion's membrane also play a part in regulating mitochondrial metabolism.
