Cell Cycle 5

Question 1

When was p16 discovered?

Answer 1

1993

Question 2

How did they discover p16?

Answer 2

2 yeast hybrid with cdk4

Question 3

What is the structure of p16?

Answer 3

4 Ankyrin repeats

Question 4

What are family members of p16?

Answer 4

p15, p18, p19

Question 5

What mutation made p16 unable to bind?

Answer 5

P114L

R87P

Question 6

What happens when p16 bind cdk (structurally)?

Answer 6

Rotation of beta strand (N) lobe by 15˚. Misaligns ATP binding site that lies between C and N lobes

Question 7

Why is p16 a potent inhibitor of cell cycle?

Answer 7

p16 displaces p21, p27 and p57 which can thenbind other cdks/cyclins

Question 8

Can p16 promoter be methylated?

Answer 8

Yes - to silence it

p16 is promoter methylated or deleted in 20% of cancers

Question 9

Give an example of oncogene induced senescence?

Answer 9

Injection of Ras isn’t proliferative because it activates expression of p16 - halting proliferation

Question 10

What is replicative senescence?

Answer 10

DDR (arrest) induced because of shortening of telomeres

Question 11

What is the nucleotide telomere sequence repeat?

Answer 11

TTAGGG

Question 12

Why do cancerous cell not under replicative senescence?

Answer 12

Have telomerase action, or homologous recombination 10% of the time.

Question 13

How many bases are typically lost in replication?

Answer 13

50/200

Question 14

How long is the average telomere?

Answer 14

5-25Kb in humans

Question 15

What healthy endogenous cells have telomerases?

Answer 15

Germline cells and stem cells

Question 16

Why do most somatic cells not require telomerases?

Answer 16

They do not replicate

Question 17

Are we pombe cells?

Answer 17

We are not - they have circular DNA and so do not require telomerases

Question 18

Why were ciliated protozoa key in discovery of telomerases?

Answer 18

They have many small chromosomes and can’t not go into replicative senescence because they are single celled organisms

Question 19

What is the catalytic domain of telomerase?

Answer 19

hTERT

Question 20

How does telomerase work?

Answer 20

Uses RNA strand to catalyse the addition of DNA to the other DNA strand. DNA polymerase fill in the other strand

Question 21

Why is the replicative senescence 6-9 days after addition of telomerase inhibitor peculiar?

Answer 21

Would not expect telomer to be a at a critical length after 6-9 replications, hence telomerase must affect some other pathway

Question 22

What is the function of AZT?

Answer 22

Thymidine analogue - has no -OH 3’ and so can not be extended - prevents action of telomerase

Question 23

What are the side affects of AZT?

Answer 23

Infertility, reduced blood circulation (stem cells unable to replenish)

Question 24

Other than telomerase, how can telomeres be maintained in cancer?

Answer 24

ALT pathway (homologous recombination)