Cell death

Question 1

What is necrosis?

Answer 1

-large scale form of cell death
-stems across tissue - 1 cell dying induces surrounding cells to die
-more than 1 mechanism of cell death may be involved

Question 2

What causes necrosis to occur?

Answer 2

-physical damage - trauma, extreme temp
-toxins - external (snake venom), internal (bacterial toxins)
-acute hypoxia/ischaemia - stroke

Question 3

What is apoptosis?

Answer 3

Programmed cell death - cell suicide

Question 4

What causes apoptosis to occur?

Answer 4

-physiological situations - tissue size maintenance, developmental cell loss, removal of immune cells
-pathological situations - DNA damage, virally infected cells

Question 5

What are the reversible characteristics of necrosis?

Answer 5

-membrane integrity compromised
-organelle + cell swelling

Question 6

What are the irreversible characteristics of necrosis?

Answer 6

-increased intracellular Ca2+
-autolysis - destruction of cells by their own enzymes
-cell lysis - bursting
-elicits an inflammatory response - contents of cell spilled into tissue

Question 7

What are the characteristics of apoptosis?

Answer 7

-shrinkage
-nuclear breakdown
-apoptotic bodies - vesicles containing dying parts of cells
-phagocytosis
-no inflammatory response
-requires energy

Question 8

When is developmental apoptosis used?

Answer 8

-metamorphosis
-digit formation in mice
-the brain

Question 9

What are C-elegans involved in?

Answer 9

Involved from recognition of apoptotic signals to engulfment of apoptotic cells by phagocytosis

Question 10

What does decreased Ced 3 or 4 result in?

Answer 10

Excess adult cells

Question 11

What does decreased Ced 9 result in?

Answer 11

Massive cell death

Question 12

What are caspases and why are they called that?

Answer 12

-the executioners of cell death - essential for apoptosis
-irreversible pathway
-C = cysteine at their active site
-Asp = aspartic acids are the cleavage site in target proteins

Question 13

What are initiator caspases?

Answer 13

-activated by apoptotic signals
-activate executioner caspases
-1 initiator caspase can activate multiple executioner caspases

Question 14

What are executioner caspases?

Answer 14

-cleave more than 1000 proteins
-critical for all sorts of processes
-disruption gives rise to apoptotic features

Question 15

What are the targets of caspases?

Answer 15

-cause breakdown of nucleus structure
-prevents DNA repair - cleaves DNA repair enzyme PARP
-causes cytoskeletal changes

Question 16

What are the 2 ways that apoptosis can be activated?

Answer 16

-extrinsic pathway
-intrinsic pathway

Question 17

Describe the extrinsic pathway for apoptosis activation

Answer 17

-tumour necrosis factor family
-6 related receptors (death receptors)
-death-inducing signalling complex (DISC) activates initiator caspases

Question 18

What is DISC?

Answer 18

A multi-protein complex formed by members of the ‘death receptor’ family of apoptosis-inducing cellular receptors

Question 19

What triggers the intrinsic pathway for apoptosis activation?

Answer 19

-stress signals e.g DNA damage
-developmental signals

Question 20

Describe the intrinsic pathway for apoptosis activation

Answer 20

-apoptotic signal from cell causes cytochrome C to be released
-causes Apaf1 to become activated + form apoptosome (protein complex)
-recruits initiator caspases, bringing them together so they can cleave themselves + become active
-if the balance of pro-apoptotic factors + anti-apoptotic factors shift towards pro, then cytochrome C is released