cell cycle

Question 1

what are the 4 main divisions of the cell cycle

Answer 1

g1 phase, s phase, g2 phase, cell division

Question 2

what does the s stand for in the s phase

Answer 2

synthesis

Question 3

why do cells enter the G0 phase

Answer 3

if there are insufficient nutrients, or the cell has become terminally differentiated (such as nerve cells as they cannot replicate)

Question 4

under what situation is the G0 phase reversible

Answer 4

lack of nutrients, can re-enter the cell cycle after a return to the normal level

Question 5

under what situation is the G0 phase irreversible

Answer 5

differentiation or senescence (gradual deterioration of the cells)

Question 6

what is the typical length of the Mitotic stage of the cell cycle

Answer 6

1 hour

Question 7

what is the typical length of the G1 stage of the cell cycle

Answer 7

5-6 hours

Question 8

what is the typical length of the S stage of the cell cycle

Answer 8

10-12 hours

Question 9

what is the typical length of the G2 stage of the cell cycle

Answer 9

4-6 hours

Question 10

when do cells divide

Answer 10

when given signals
under suitable conditions

Question 11

what are the 3 main check points in the cell cycle

Answer 11

1- G2/M
2- spindle checkpoint
3- G1

Question 12

what is the G2/M checkpoint looking for

Answer 12

DNA damage

Question 13

what is the spindle checkpoint looking for

Answer 13

that chromosomes are correctly attached to the mitotic spindle

Question 14

what is the G1 checkpoint looking for

Answer 14

correct cell size, sufficient nutrients, DNA damage, growth factors

Question 15

what enzyme controls the cell cycle control

Answer 15

cyclin dependant kinases (Cdk’s)

Question 16

what do protein kinases phosphorylate

Answer 16

other proteins

Question 17

how do Cdk’s become active

Answer 17

if its coupled to cyclin

Question 18

which cyclins are expressed during the G1 phase

Answer 18

cyclin D and cyclin E

Question 19

which cyclins are expressed during the S phase

Answer 19

Cyclin D, E, A and B

Question 20

which cyclins are expressed during the G2 phase

Answer 20

cyclin A, B, and D

Question 21

which cyclins are expressed during the Mitosis phase

Answer 21

Cyclin A, B, and D

Question 22

the G2M is controlled by what?

Answer 22

MPF (maturation promoting factors)

Question 23

what is the MPF made up of

Answer 23

Cyclin B and Cdk 1

Question 24

what are the stages of MPF regulation

Answer 24

MPF gets dephosphorylated (looses 2 phosphate groups)
MPF then becomes active allowing cells to under go mitosis
Cyclin B then degrades leaving Cdk 1
Cdk1 is then dephosphorylated again
synthesis of cyclin B occurs and the 2 bind
and get phosphorylated by 3 phosphate groups and they’ve now become MPF again

Question 25

what does the spindle checkpoint look for

Answer 25

- ensures chromosomes are aligned correctly ( one chromatid to each pole via kinetochores)

Question 26

what is the spindle checkpoint controlled by

Answer 26

APC - anaphase promoting complex

Question 27

what is APC activated by

Answer 27

MPF

Question 28

what happens when APC is activated

Answer 28

it activates enzymes that break down protein complex at the centromere

Question 29

what is the G1/S checkpoint driven by

Answer 29

retinoblastoma protein (pRb - is also a tumour suppressor gene ) and E2F

Question 30

how can pRB become activated after an injury

Answer 30

when injured a signal is released from the area e.g. wounding, where blood platelets release PDGF (platelet derived growth factor) - this causes PDFG to bind to receptors on the skin fibroblasts - this stimulates the production of Cyclin D - Cyclin D binds to Cdk and activates enzymes - stimulate skin fibroblasts to divide so progression occurs from G1 to S - causing the wound to be repaired

Question 31

what is the role of Rb in the G1/S

Answer 31

pRb associates with E2F in G0 and early G1 blocking the transactivation domain

Question 32

in what cancers is the Rb mutated

Answer 32

retinoblastoma

Question 33

what is the stages of normal P53 function

Answer 33

1- DNA damage is noticed 2- cell division stops and p53 triggers enzyme to repair damage 3- P53 triggers the destruction of cells damaged beyond repair

Question 34

what is the stages of abnormal P53 function

Answer 34

1- DNA damage is noticed 2- P53 fails to stop cell division, so cells continue to divide 3- continual division occurs, if another damage is sustained the cell may become cancerous

Question 35

why are elephants less susceptable to cancer

Answer 35

they have more copies of p53 (40 copies) the elephants cells kill mutated cells rather than trying to repair them