Apoptosis is a programmed form of cell death involving the degradation of cellular constituents by a group of cysteine proteases called caspases. The caspases can be activated through either the intrinsic (mitochondrial mediated) or extrinsic (death receptor mediated) apoptotic pathways.
The intrinsic apoptotic pathway is characterized by permeabilisation of the mitochondria and release of cytochrome c into the cytoplasm. Cytochrome c then forms a multi-protein complex known as the ‘apoptosome’ and initiates activation of the caspase cascade through caspase 9.
The extrinsic apoptotic pathway is activated by death receptors on the plasma membrane such as tumour necrosis factor receptor 1 (TNFR1) and Fas/CD95. As ligands bind to these receptors, the death inducing signaling complex (DISC) is formed leading to initiation of the caspase cascade through caspase 8.
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