Explain in detail extrinsic and intrinsic mechanism of apoplosis.
Answers
Intrinsic Pathway
The intrinsic pathway mainly triggers apoptosis in response to internal stimuli:
Biochemical stress
DNA damage (this activates the p53 gene – which halts the cell cycle and initiates DNA repair. If this repair attempt is unsuccessful, apoptosis can be induced)
Lack of growth factors
The intrinsic pathway is modulated by two groups of molecules, Bcl-2 and Bax. Activation of Bax leads to the formation of Bax-Bax dimers, which in turn enhances the action of a variety of apoptotic stimuli – increasing a cell’s susceptibility to apoptosis. The Bcl-2 family consists of both pro- and anti-apoptotic members, and it is the balance between these that determines how susceptible a cell may be to apoptosis.
The balance between these groups of molecules establishes a ‘molecular switch’ which determines whether a cell will survive or undergo apoptosis in response to internal stimuli,
Extrinsic Pathway
The extrinsic pathway triggers apoptosis in response to external stimuli, namely by ligand binding at ‘death’ receptors on the cell surface.
These receptors are typically members of the Tumour Necrosis Factor Receptor (TNFR) gene family, such as TNFR1 or FAS. Binding at these receptors leads to receptor molecules grouping up on the cell surface to initiate downstream caspase activation.
Thankyou