BSC 422 Lecture Notes - Lecture 18: Cytotoxic T Cell, Apaf1, Fas Ligand
22 May 2018
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Mechanism of Apoptosis:
There are generally three different mechanisms for apoptosis. These
are:
1. Triggered by internal signals, i.e., signals arising within the cell.
2. Triggered by external signals.
3. By Apoptosis-Inducing Factor (AIF).
1. By Internal Signals:
In a normal cell, the protein (BC1-2) produced from a gene BC1-2 remains on the
outer surface of the mitochondria. The protein BC1-2 holds the apoptotic
protease activating factor- 1 (Apaf-1). But when the damage occurs in the cell
internally due to some reactive oxygen, the Apaf-1 factor is released from BC1- 2-
Apaf-l complex.
This allows the protein Bax to penetrate the mitochondrial membrane causing a
leakage of cytochrome C from the mitochondria.
Then the released cytochrome C and Apaf-1 bind to molecules of caspase 9. The
complex containing cytochrome C, Apaf- 1, caspase 9 and ATP is called
Apoptosome. Caspase 9 is actually one form of protease which cleaves proteins at
Aspartic acid residues.
The caspase 9 activates other caspases creating a cascade of proteolytic activity
which leads to the lysis of cell through digestion of structural proteins of the
cytoplasm and degradation of chromosomal DNA.
2. External Signals:
Some receptor proteins (FAS and TNF) and other molecules residing on the
surface of the cell are responsible for apoptosis. when cytotoxic T cells containing
complementary factor FASL bind to the target cell, FASL binds with the FAS of
the target cell leading to the death of the cell by apoptosis.
3. Apoptosis-Inducing Factor (AIF):
This AIF is a protein located in the inter-membrane space of mitochondria. When
the cell receives the signal for its death, AIF is released from the mitochondria to
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Document Summary
There are generally three different mechanisms for apoptosis. These are: triggered by internal signals, i. e. , signals arising within the cell, triggered by external signals, by apoptosis-inducing factor (aif), by internal signals: In a normal cell, the protein (bc1-2) produced from a gene bc1-2 remains on the outer surface of the mitochondria. The protein bc1-2 holds the apoptotic protease activating factor- 1 (apaf-1). But when the damage occurs in the cell internally due to some reactive oxygen, the apaf-1 factor is released from bc1- 2- This allows the protein bax to penetrate the mitochondrial membrane causing a leakage of cytochrome c from the mitochondria. Then the released cytochrome c and apaf-1 bind to molecules of caspase 9. The complex containing cytochrome c, apaf- 1, caspase 9 and atp is called. Caspase 9 is actually one form of protease which cleaves proteins at.
