cell cycle regulation

Question 1

what are the stages of the cell cycle?

Answer 1

G1, G0, S, G2, M (includes mitosis and cytokinesis)

Question 2

what is the key event in mitosis?

Answer 2

the metaphase to anaphase transition

Question 3

combining a cell in S phase with one in G1 phase results in?

Answer 3

both cells pass S and replicate DNA

Question 4

combining a cell in S phase with one in the G2 phase results in?

Answer 4

only the S phase nucleus replicating DNA because the G2 nucleus cannot move backwards back into S

Question 5

what are the conditions that must be respected when working with yeast

Answer 5

the effect of the mutation is viable and can be seen only is specific conditions, such as single-gene temperature sensitive mutants that stop dividing at restrictive temps

Question 6

what is the advantage of xenopus as a study?

Answer 6

all embryos are synchronized, and cleavage occurs even without DNA replication

Question 7

what is the domino hypothesis?

Answer 7

the events of the cell cycle must be completed for the next phase to begin

Question 8

what is the clock/timer hypothesis?

Answer 8

that events of the cell cycle must be completed in a certain timeframe after which the cell even if it hasn’t completed that phase it will enter the next phase

Question 9

explain how the cell cycle is controlled

Answer 9

by both the Clock (biochemical switches turn on specific events in a certain order and at a certain time) and the Domino (internal and external factors modulate the clock if the phase hasn’t been completed)

Question 10

what are the components of the MPF?

Answer 10

a kinase and a cyclin

Question 11

when are CDK’s active?

Answer 11

only when they are bound to the regulatory protein cyclin (this is always present in the cell at varying concentrations)

Question 12

CDK and cyclin work together as?

Answer 12

a kinase

Question 13

when is cyclin at its highest concentration?

Answer 13

it starts to accumulate at interphase (G1,S,G2) and peaks at mitosis and then falls

Question 14

when is cyclin D and E present

Answer 14

at G1

Question 15

when is cyclin A present?

Answer 15

at S and G2 and some of M

Question 16

when is cyclin B present

Answer 16

at the first half of mitosis

Question 17

how is cyclin-CDK activity regulated?

Answer 17

by degradation of cyclin’s by proteolysis, by modulation by de/phosphorylation. CDK inhibitors

Question 18

what is responsible for the oscillation of the cyclin levels?

Answer 18

the regulated proteasome-mediated degradation, the ubiquitin chain can degrade a cyclin

Question 19

what is the function of Wee1 kinase?

Answer 19

inhibition of mitotic CDK-cyclin complex

Question 20

what is the purpose of Cdc25 phosphatase?

Answer 20

activation of mitotic CDK-cyclin complex

Question 21

what are the 2 inhibitor families?

Answer 21

Cip/Kip (p21) which act in G1 and S phase, and Ink4 which is selective inhibition of cdk D cyclin complexes acting in G1

Question 22

inhibition of CDK do what?

Answer 22

they block entry to S phase

Question 23

inhibition of cyclin degradation results in?

Answer 23

delays exit from mitosis (it is and inhibition of APC activation)

Question 24

what does inhibition of activating phosphatase do?

Answer 24

blocks the entry to mitosis

Question 25

name the 3 check points for the cell cycle

Answer 25

the start or restriction checkpoint (G1/S), the G2/M checkpoint, the metaphase/anaphase checkpoint

Question 26

what are the conditions checked at the G1/S point

Answer 26

If the environment is favorable. There is nutrient availability, there are growth factors/mitogens, cell size is fine, DNA integrity, note that CDK are inactive in G1

Question 27

what are the conditions looked for at G2/M point

Answer 27

is all DNA replicated, is all DNA damage repaired

Question 28

what at the conditions of the Metaphase/anaphase point

Answer 28

are all the chromosomes properly attached to the mitotic spindle

Question 29

progress past the G1/S checkpoint depends on Rb. How?

Answer 29

one of the substrates of G1 cyclin-cdk complex is Rb protein, normally rb inhibits entrance into S , phosphorylation inactivates Rb so that the cells can enter S

Question 30

what is the role of p53

Answer 30

if DNA is damages then the p53 protein blocks the cell cycle and it is a transcription factor which promotes transcription of CDK inhibitor (p21)

Question 31

explain the control of the G2/M point

Answer 31

the mitotic-cdk complex are kept inactive by phosphorylation done by Wee1 kinase, when conditions are ok the mitotic cdk complex id dephosphorylated, the cell can now enter mitosis

Question 32

how does mitotic cyclin-cdk complex induce entry into mitosis

Answer 32

by inducing the breakdown of the nuclear envelope, by inducing chromosome condensation, by inducing mitotic spindle assembly

Question 33

what is the APC

Answer 33

the activation of the anaphase promoting complex is a needed event in order to pass from metaphase to anaphase. APC is a ubiquitin ligase so it marks proteins for proteasome mediated degrading, its targets are securing and cyclin.

Question 34

APC activates separase

Answer 34

APC kept inactive by spindle checkpoint proteins

2. APC is activated by mytotic cyclin/Cdk complex
3. APC send securin to degradation
4. Separase is active and remove cohesins holding together sister chromatids

Question 35

what are the best organisms to study the cell cycle

Answer 35

budding yeast and fission yeast (S. cerevisiae, S.Pombe), sea urchins, cams, frogs, mammalian cell cultures