Cell death

Question 1

What is necrosis?

Answer 1

‘whole-scale’ form of cell death, 1 cell induces surrounding

Question 2

What is apoptosis?

Answer 2

programmed, very specific and limited cell death

Question 3

When does necrosis occur?

Answer 3

Physical damage
- Trauma e.g cuts, burns
- Extreme temp e.g frostbite
Toxins
- External e.g snake venom
- Internal e.g bacterial toxins
Acute hypoxia/ischaemia e.g stroke

Question 4

Describe how necrosis can be reversible

Answer 4

Membrane integrity compromised
Organelle and cell swelling

Question 5

Describe how necrosis can be irreversible

Answer 5

Increase intracellular calcium
Autolysis
Cell bursting (lysis)
Elicits an inflammatory response

Question 6

When does apoptosis occur? Give some examples

Answer 6

Physiological situations:
- Tissue size maintenance
- Developmental cell loss - growth factors
- Removal of immune cells
- Hormone dependent involution e.g menstruation
- Inappropriate interactions - Anoikis
Pathological situations:
- DNA damage e.g radiation, oxidative stress
- Virally infected cells

Question 7

List the characteristics of apoptosis

Answer 7

• Cell shrinkage
• Nuclear breakdown
• Apoptotic bodies → vesicles containing dying parts of cells
• Phagocytosis
• No inflammatory response
• Controlled so requires energy
• Relationship with autophagy

Question 8

Give some examples of developmental apoptosis in organisms.

Answer 8

Metamorphosis e.g tadpole → frog
- Surge in thyroid hormones in the blood initiate apoptosis in tail cells
Digit formation in mice
- Apoptosis initiated through release of local signal proteins

Question 9

Compare apoptosis and necrosis.

Answer 9

Apoptosis:
- Genetic programmed
- Controlled
- Shrinkage
- Membrane integrity maintained
- packaged into apoptotic bodies
- ATP required
- no inflammatory response

Necrosis:
- Ischemia, trauma or ATP depletion
- Uncontrolled
- Swelling
- Mem integrity collapsed
- Leakage to extracelluar fluid
- ATP not required
- Inflammatory response

Question 10

What are Ced genes involved in?

Answer 10

involved from recognition of apoptotic signal to engulfment by phagocytes

Question 11

What are caspases?

Answer 11

enzymes that are essential to apoptosis

Question 12

Describe initiator caspases

Answer 12

Activated by apoptotic signals
Active executioner caspases

Question 13

Describe executioner caspases

Answer 13

Cleave >1000 proteins
Very promiscuous → can get big effect from triggering them
Amplify proteolytic cascade
One initiator caspase can activate multiple executioner caspase

Question 14

What are the targets of caspases?

Answer 14

• Cause breakdown of nucleus struc. Including the nuclear lamina through cleavage of nuclear lamins
• Prevents DNA repair enzyme PARP (Poly-ADP-ribose polymerase)
• Cause cytoskeletal changes, for example the breakdown of actin, by cleaving cytoskeletal proteins like Gelsolin

Question 15

What is the extrinsic pathway in apoptosis triggered by?

Answer 15

External factors e.g immune cells
caspase 8

Question 16

What is the intrinsic pathway in apoptosis triggered by?

Answer 16

Stress signals from inside the cell e.g DNA damage, oncogenes, hypoxia
Also, developmental signals
caspase 9