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Apoptosis is a type of cell-death. In contrast to necrosis, apoptosis is a process initiated by the cell itself.

Apoptosis takes place as part of cell-internal processes and hence does not harm surrounding cells. It is a two-phase process, divided into the initiation- and the effector phase. The initiation phase can further be divided into the extrinsic pathway (type 1 apoptosis) and the intrinsic pathway (type 2 apoptosis). The extrinsic pathway takes place via the trimerisation of a receptor of the TNF-alpha family, denominated the death receptor. Subsequently, the trimers bind adaptor-molecules that are bound via a domain that is called the death-domain. By recruitment of the proteins TRADD and FADD the caspase cascade is triggered via caspase 8, ultimately leading to a feedback that causes activation of further caspase 8 molecules.

Image: Immunofluorescence of human dermal fibroblasts stained with Lamin A/C (clone jol3)

The intrinsic pathway apparently occurs due to release of cytochrome C from the mitochondria into the cytoplasm. Severe DNA damage, for instance, can trigger this pathway via the tumor suppressor p53. The protein p53 stimulates expression of pro-apoptotic factors like the Bcl-2 protein family.

The effector phase eventually leads to cell death. One of the molecular effects leading to cell death is that lamin and actin are degraded.

Hint: On you find more than 12,000 antibodies for research on apoptosis and necrosis

David Kitz Kramer
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