Lecture 22: Apoptosis-programmed cell death Flashcards
Programmed Cell Death
• Programmed cell death is a vital process to the overall good of a multicellular organism
- Apoptosis is one form of programmed cell death
- Up to half of the neurons in a developing vertebrate organism die soon after they are formed (target selection)
- Some tissues are formed and most are maintained at a consistent size by selective apoptosis
Morphological changes during apoptosis
- Cells shrink in size
- Chromatin condenses and fragments
- The cytoskeleton disassembles
- The nuclear envelope collapses
- The cell surface distends or “blebs”
- The plasma membrane is chemically altered to promote phagocytosis
____ results from acute injury and the cells typically swell and burst causing an inflammatory response.
Cell necrosis
_____ are essentially degraded from the inside out without damage to neighboring cells
Apoptotic cells
Cell death is induced by the absence or low amounts of “_______”
survival factors
Biochemical changes associated with apoptosis
- DNA fragmentation
- Loss of phospholipid asymmetry in the plasma membrane.
– Phosphatidylserine flips to the outer leaflet
- Cell surface modifications that promote phagocytosis
- Loss of Proton Motive force in mitochondria
- Some of these changes can be detected in dying cells
_____ that are activated as a result of apoptosis cut genomic DNA into a characteristic ladder patterns due to cleavage in the linker regions between nucleosomes
Endonucleases
How does the TUNEL assay detect apoptosis?
The newly generated DNA ends that result from genomic cleavage can be detected in cells by modifying the ends of DNA with a fluorescent nucleotide.
TUNEL=TdT mediated dUTP nick end labeling
TdT=terminal deoxynucleotide transferase
____ is responsible for the apoptosis that is involved in limb formation
BMP
The primary mechanism of destruction is the activation of proteases called ____ (active site cys, cleave at specific asp residues)
caspases
Not all caspases are involved in apoptosis, some are important for the _____
inflammatory response
An activation cascade is thought to be set in motion by _____ that are activated in response to a signal through their _____.
initiator caspases
caspase recruitment domain (CARD)
Once activated, these initiator caspases propagate the cascade of activation through ______
executioner caspases
Caspases involved in inflamation
– Caspase 1 (Interleukin-1 converting enzyme, ICE), 2, 4
Initiator caspases
– Extrinsic pathway
• Caspases 8, 10
– Intrinsic pathway
• Caspases 2, 9
Executioner Caspases
– Caspases 3, 6, and 7
Activation of Caspases
Caspase Cascade
How do caspases trigger DNA fragmentation
-executioner caspases cleave iCAD, cleave iCAD releases CAD which cuts DNA between nucleosomes
Extrinsic pathway
– Activation of Cell surface receptors (death receptors)
Intrinsic pathway
– Triggered in response to injury or stress
– DNA damage
– Lack of oxygen, nutrients, or survival signals
Extrinsic pathway of Apoptosis
- Cell surface receptors (death receptors) activate the extrinsic pathway
- Single span membrane proteins with an extracellular ligand binding domain and an intracellular death domain
- Receptors are homotrimers of the tumor necrosis factor (TNF) family
- Includes the TNF receptors itself and the Fas death receptor
Induction of apoptosis by extracellular stimuli
Extrinsic pathway by activation of Fas death receptors
Intrinsic Pathway of Apoptosis
- Depends on the release of mitochondrial intermembrane space proteins into the cytosol
- The release of cytochrome c, the electron carrier between ETS complex III and cytochrome oxidase, can trigger apoptosis
- Released cytochrome c binds to a procaspase activating adapter called Apaf-1 (apoptotic protease activating factor), driving its oligomerization into a wheel like heptamer called the apoptosome
- The aggregated Apaf-1 binds and activates caspase-9 by induced proximity
- This initiator caspase-9 activates downstream executioner caspases
