Figure 1.

The extrinsic and intrinsic pathways of apoptosis. Taken and modified from D’Arcy [12]. The extrinsic pathway is triggered by external stimuli or ligand molecules, particularly involving death receptors. The intrinsic pathway is mediated by Bax/Bak pore formation into the mitochondrial membrane. Subsequently, cytochrome c is released and combines with apoptotic protease activating factor-1 (Apaf)–1 and procaspase-9 to form the apoptosome. Both pathways converge in activating executioner caspases -3, -6, and -7.