Prodomains are cleaved off; from two polypeptides, we get one multiprotein complex. Apoptotic cells also change their cell surface properties. Phosphatidylserine is normally in the inner leaflet; in apoptotic cells, it flips to the outer leaflet. In vivo macrophages recognizes the exposed lipid and phagocytose the cell. In experiments probe for phosphatidylserine to detect for apoptotic cells. How to initiate the process: extrinsic started via death receptors, eg. killer lymphocyte tells a cell to undergo apoptosis. Fas ligand (trimer) activates the fas death receptor. This activates the death domains of the fas death receptor. Fadd (adaptor protein) binds to the death domain. Apoptosome: this apoptosome as a whole goes around to activate caspase-3. Has a ligand-binding domain but not a death domain. Can outcompete functional fas death receptors for ligands. Mimic an initiator caspase that lacks a proteolytic domain. Other inhibitors simply block the apoptotic machinery.