apoptosis and cellular senescence

Question 1

who coined the word apoptosis

Answer 1

wyllie and currie who worked on tumour histopathology un edinbrugh

Question 2

what is necrosis

Answer 2

cell death following injury, infection it provokes the immune response while apoptosis does not.

Question 3

name markers for apoptosis

Answer 3

-cell morphology
-DNA ladders
-tunel assay: label termini DNA fragments with fluorescent group by enzyme terminal transferase.
-binding of annexin v to cells. this is caused by membrane changes and is assayed in flow cytometer.
-activation by caspase enzymes which is followed by assaying by western blotting.

Question 4

name the 3 stages of apoptosis and what is involved in each one

Answer 4

decision: survival factors, TNF,Fas, Bcl-2 family, p53, DNA damage
execution: caspases, nucleases, surface modifications.
death: phagocytosis.

Question 5

how are caspases expressed

Answer 5

as pro enzymes which require activation

Question 6

what are the 3 domains in a caspase

Answer 6

N-terminal, large, small

Question 7

how are caspases activated by proteolytic cleavage between domains

Answer 7

the large and small subunit form heterodimers. the activation site between large and small domains is a caspase recognition site. this results in a caspase cascade

Question 8

what is the result of caspases being very specific

Answer 8

they recognise and degrade very few proteins. it is highly effective.

Question 9

what do initiator caspases do

Answer 9

activate a cascade resulting in activation of executioner caspases

Question 10

how are caspases 8 and 10 activated

Answer 10

by death receptors via FADD

Question 11

how is caspase 9 activated

Answer 11

by APAF-1, cytochrome C, and ATP via the caspase recruitment domain. initiated by intracellular events such as p53

Question 12

what do caspase 7 and 3 do

Answer 12

induce cell killing

Question 13

how do caspase inhibitors work

Answer 13

bind to catalytic site of caspases.

Question 14

what does c-FLIP (flice inhibitory protein) do

Answer 14

inhibits caspase 8. over expression of this protein is common in tumours resistant to death inducing signals such as TRIAL

Question 15

describe the function of FADD

Answer 15

recruited from the cytoplasm. binds through death domain cluster. it acts as a adapter protein. it also has a death effector domain. binds molecules like caspase 8 and 10. causes activation of initiation of apoptosis.

Question 16

hoe do death receptors signal death

Answer 16

bind to cytotoxic lignads

Question 17

what mechanism prevent external death signals

Answer 17

soluble decoy receptors, membrane bound decoy receptors, intracellular signalling activators and inhibitors.

Question 18

how is death receptor activated

Answer 18

ligand binding, receptor trimerization, intracellular death domain cluster signals pro-apoptotic signal

Question 19

what are the BCL-2 family and where are they found and what is there structure

Answer 19

anti-apoptotic, in B cell lymphocytes, 25-26 Kda membrane protein.

Question 20

name some homologues of BCL-2

Answer 20

BAX, forms heterodimers with bcl-2 and inactivates bcl-2

Question 21

name the classes of the bcl-2 family proteins and examples for each one

Answer 21

anti-apoptotic BCL-2 :bcl-2, bcl-XL
pro-apoptotic BH123: Bax, Bak
pro-apoptotic BH-3 only: Bad, Bim, Bid, Puma, Noxa.

Question 22

what is PUMA

Answer 22

p53 upregulated modulator of apoptosis.

Question 23

in the intrinsic pathway how is cytochrome C released

Answer 23

the BH123 proteins aggregate and act as the apoptotic stimulus

Question 24

what protein prevents the BH123 proteins from coming together

Answer 24

the active anti-apoptotic Bcl-2 protein

Question 25

what protein inactivates the anti-apoptotic Bcl-2 protein

Answer 25

the activated BH3 only protein

Question 26

name the cellular inhibitors of apoptosis

Answer 26

c-FLIP, Survivin( upregulated in cancer)

Question 27

name viral inhibitors of apoptosis

Answer 27

Adenovirus E1B-19kDa protein, Baculoviral IAP

Question 28

what sequence repeat do telomeres have and what is there structure

Answer 28

TTAGGG. the repeat extends for up to 12KB. it has a G rich single strand that forms a terminal 3’ overhang. it is non-coding DNA

Question 29

name the functions of telomeres

Answer 29

protect chromosomes, prevent ends from becoming entangled, assist in pairing of homologous chromosomes in prophase.

Question 30

describe the synthesis of telomeres by telomerase

Answer 30

telomerase has component with enzymatic activity of specialised reverse transcriptase. also contains telomerase RNA component which provides AAUCCC template to guide insertion of TTAGGG

Question 31

where is telomerase usually found

Answer 31

germline cells, adult stem cells, progenitor cells, cancer cells, unicellular eukaryotes

Question 32

what are the clinical implications

Answer 32

cancer and aging

Question 33

how is cellular senescence induced

Answer 33

telomere shortening blocks cell division. contributes to aging. prevents cancer.
cancer cells synthesis telomerase to prevent telomere shortening.