Senescence: Difference between revisions

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Senescence (view source)

Revision as of 07:25, 30 May 2007

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{| border="1" cellpadding="2"  
{| border="1" cellpadding="2"  
!width="20"| '''Space'''  
!width="20"| '''External Signals'''  
!width="20"| '''Time'''  
!width="20"| '''Internal Signals'''
!width="20"| '''Inducing Factors'''
|-  
|-  
|   
|  Fas and the TNF receptor are integral membrane proteins with their receptor domains exposed at the surface of the cell
binding of the complementary death activator (FasL and TNF respectively) transmits a signal to the cytoplasm that leads to
|  In a healthy cell, the outer membranes of its mitochondria display the protein Bcl-2 on their surface.
|  In a healthy cell, the outer membranes of its mitochondria display the protein Bcl-2 on their surface.
|
|-  
|-  
|  
| Activation of caspase 8
| Internal damage to the cell (e.g., from reactive oxygen species) causes  
| Internal damage to the cell (e.g., from reactive oxygen species) causes  
Bcl-2 to activate a related protein, Bax, which punches holes in the outer mitochondrial membrane, causing  
Bcl-2 to activate a related protein, Bax, which punches holes in the outer mitochondrial membrane, causing  
cytochrome c to leak out.
cytochrome c to leak out.
|
|-
| Caspase 8 (like caspase 9) initiates a cascade of caspase activation leading to
phagocytosis of the cell.
| The released cytochrome c binds to the protein Apaf-1 ("apoptotic protease activating factor-1").
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|-
|
| Using the energy provided by ATP, these complexes aggregate to form apoptosomes.
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|-
|
|The apoptosomes bind to and activate caspase-9.
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|-
|
| Caspase-9 is one of a family of over a dozen caspases. They are all proteases. They get their name because they cleave proteins — mostly each other — at aspartic acid (Asp) residues).
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|-
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| Caspase-9 cleaves and, in so doing, activates other caspases (caspase-3 and -7).
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|-  
|-  
|  
|  
| The released cytochrome c binds to the protein Apaf-1 ("apoptotic protease activating factor-1").
| The activation of these "executioner" caspases creates an expanding cascade of proteolytic activity (rather like that in blood clotting and complement activation) which leads to digestion of structural proteins in the cytoplasm, degradation of chromosomal DNA, and phagocytosis of the cell.
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|}  
|}  


is released from the mitochondria (like the release of cytochrome c in the first pathway);
migrates into the nucleus;
binds to DNA, which
triggers the destruction of the DNA and cell death.


Using the energy provided by ATP,
these complexes aggregate to form apoptosomes.
The apoptosomes bind to and activate caspase-9.
Caspase-9 is one of a family of over a dozen caspases. They are all proteases. They get their name because they cleave proteins — mostly each other — at aspartic acid (Asp) residues).
Caspase-9 cleaves and, in so doing, activates other caspases (caspase-3 and -7).
The activation of these "executioner" caspases creates an expanding cascade of proteolytic activity (rather like that in blood clotting and complement activation) which leads to
digestion of structural proteins in the cytoplasm,
degradation of chromosomal DNA, and
phagocytosis of the cell.




Tcrain
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