apoptosis

Question 1

what is apoptosis?

Answer 1

a form of programmed cell death

Question 2

what are some examples of processes requiring apoptosis?

Answer 2

developing mouse paws
making anthropod joints

Question 3

what is the difference between necrotic cells and apoptotic cells?

Answer 3

necrotic cells spill their contents into their neighbors
apoptotic cells die neatly without damaging their neighbors

Question 4

what are caspases?

Answer 4

mediate the proteolytic cascade necessary for apoptosis - they chop up proteins in cell (use sulfur atom in cysteine to perform cleavage)

Question 5

how does apoptosis start?

Answer 5

initiator caspases activate executioner caspases

Question 6

how are caspases synthesized and activated?

Answer 6

synthesized in cell as inactive precursors (procaspases) and activated by cleavage

Question 7

what are initiator caspases?

Answer 7

inactive monomers that are activated when they dimerize and self-cleave

Question 8

what other enzymes does caspase activate?

Answer 8

DNAse -> catalyzes the hydrolytic cleavage of DNA

Question 9

what are the two pathways of apoptosis activation?

Answer 9

extrinsic - signalled from outside
intrinsic - signalled from mitochondria

Question 10

what triggers the extrinsic pathway of apoptosis?

Answer 10

cell-surface death receptors that activate and expose death domains on receptor tails, which bind FADD (adaptor protein) which recruit copies of inactive initiator caspases (this is called the death-inducing signalling complex (DISC))

Question 11

what triggers the intrinsic pathway of apoptosis?

Answer 11

response to developmental signals or injury (like DNA damage) releases cytochrome C from mitochondria to cytoplasm which binds to Apaf1 and exposes an oligomerization domain and a caspase recruitment domain and forms apoptosome, then are activated by dimerization

Question 12

what prevents inappropriate caspase activation?

Answer 12

caspase inhibitor proteins called IAPs

Question 13

what are the main regulators of intrinsic pathway apoptosis and what do they do?

Answer 13

Bcl2 proteins
pre-apoptotic -> make holes in mitochondrial membrane
anti-apoptotic -> inactivate the pro-apoptotic Bcl2

Question 14

what do neighbour cells do during apoptosis?

Answer 14

phagocytose and digest the apoptotic cells

Question 15

how do cells recognize apoptotic cells?

Answer 15

apoptotic cells have PtdSer outside (caspases degrade a flippase that keeps PtdSer inside the cell)