PROGRAMMED CELL DEATH

Question 1

Why is plant cell death in animals and plants important?

Answer 1

Sculpting structure like hands
development
elimination of unwanted cells
regulation of cell numbers

Question 2

Describe features of necrosis (animals)

Answer 2

External triggers so no specific
No signal transduction
Causes dysfunction of organelles and plasma membrane

Question 3

Describe features of apoptosis

Answer 3

Follows a predictable signal cascade triggered by signals

Plasma membrane and some organelles are kept in tact

Question 4

What triggers apoptosis?

Answer 4

-Intrinsic pathway-
1- Intracellular stress
2- Mitochondrial membrane permeabilization and cytochrome c release 
3- Apoptisome formation  
4- Caspase 9 activation 
5- Effector caspase activation 
= Apoptosis 
-Extrinsic pathway-
1- Extracellular death ligand 
2- DISC formation 
3- Caspase 8 activation 
4- Effector caspase activation 
= Apoptosis

Question 5

Differences between intrinsic and extrinsic pathway

Answer 5

1- (I) uses caspase 9 (E) uses caspase 8

2- (I) uses XIAP inhibitory protein of caspase 9 and Apoptosis (E) uses FLIP inhibitory protein of caspase 8

Question 6

Main features of extrinsic pathway

Answer 6

• DISC formation
• Activation of the caspase cascade
• Death ligands: Bind to specific receptors
• Death receptors: Part of the TNFR superfamily

Question 7

Describe the extrinsic apoptotic pathway in detail

Answer 7

• Ligand binds to death receptor
• DISC formed
• DISC activates C8 via dimerization
• FLIP can inhibit C8 formation
• C8 links to intrinsic pathway + activates C3,7…

Question 8

Describe the intrinsic pathway in detail

Answer 8

• Cytochrome c from mitochondria activates Apaf1 (which has a CARD domain) = dATP to dADP
• Apaf1 now has CARD domain and cyt c
• Apoptosome formed by release of dADP for dATP
• Procaspase 9 is recruited to complex and activated
• C9 cleaves and activates proC9 = caspase cascade = apoptosis

Question 9

How is cytochrome c released ?

Answer 9

Via Mitochondrial Membrane Permeabilization MMP

Question 10

What are the two mechanisms of MMP

Answer 10

1 = MOMP
- Proteins of BH3 family help form channels in OM
2= PTPC
- Loss of MP = swelling and rapture
- Activated by Ca2+ accumulation or BAK/BAX

Question 11

Differences between mammalian and plant PCD

Answer 11

• No true death receptors in plants
• Vacuole in PCD
• No caspases but similar