2.10: The Cell Cycle

Question 1

does DNA replication occur in mitosis

Answer 1

NO, before

Question 2

which two processes are included in M phase

Answer 2

mitosis and cytokinesis

Question 3

which are the transition to enter mitosis and which questions are asked

Answer 3

G2/M transition
is all DNA replicated? is the environment favorable?

Question 4

state the purpose of cell cycle checkpoints

Answer 4

ensure conditions are suitable for division

Question 5

which are the transition to trigger anaphase and proceed to cytokinesis and which questions are asked

Answer 5

metaphase to anaphase transition. are all chromosomes attached to the spindle?

Question 6

which are the transition to enter cell cycle and proceed to S phase and which questions are asked

Answer 6

start transition. is the environment favorable

Question 7

at a molecular level, what are checkpoints mediated

Answer 7

the controlled activity of cyclin dependent kinases (Cdks)

Question 8

what do Cdks do and what do they require

Answer 8

Cdks phosphorylate targets proteins for the cell cycle to progress, Cdks require cyclins to be active

Question 9

t/f Cdks and cyclins can be present throughout all cell cycle stages

Answer 9

false. Cdks can, cyclins are made and broken down at different cell cycle stages

Question 10

the cyclin-cdk combo controls what

Answer 10

which target proteins are phosphorylated

Question 11

S cdk phosphorylates ? at ? stage of the cell cycle

Answer 11

S cdk phosphorylates dna helicases at G1 to S stage of the cell cycle

Question 12

which cdk complex is is at the start of the cell cycle

Answer 12

G1/S cdk w G1/S cyclin

Question 13

Mcdk phosphorylates ? at ? stage of the cell cycle

Answer 13

phosphorylates lamin (nuclear envelope breakdown) and microtubule associated proteins (spindle assembly) it is in between the G2 and M

Question 14

t/f one cdk may work with multiple cyclines, but cyclins only work one stage (can be the same cdk, must be a different cyclin)

Answer 14

true

Question 15

for budding yeast, what are the cdk partner(s)
for vertebrates, what are the cdk partner(s)

Answer 15

yeast: cdk1. vertebrates: cdk2

Question 16

cyclins can be ubiquitinated, polyubiquitination marks cyclins for ________ by the _________

Answer 16

cyclins can be ubiquitinated, polyubiquitination marks cyclins for degradation by the proteasome

Question 17

if cyclins are broken down, cdks will still/no longer be active

Answer 17

no longer

Question 18

t/f if cyclins are degraded, cdks are spared

Answer 18

yes

Question 19

______ & _______ promote M-cyclin degradation

Answer 19

APC/C and Cdc20

Question 20

APC/C and Cdc20 act as an ?

Answer 20

E3 ubiquitin ligase

Question 21

which processes determines which cyclin-cdk complex is active at any time

Answer 21

synthesis and degradation

Question 22

cdks are activated by which enzyme

Answer 22

cdk activating kinase (CAK)

Question 23

cyclin is absolute required for cdk activity by exposing the _____, once it is exposed, cak can phosphorylate cdk to further activate it

Answer 23

t loop

Question 24

which enzyme reverse the effects of cyclin cdks by removing phosphorylation from proteins

Answer 24

protein phosphatases (PP2As)

Question 25

t/f pp2as usually have the same targets as cyclin-cdks

Answer 25

true - pp2a and m-cdk participate in a complex feedback loop

Question 26

m-cdk and pp2a compete for the same targets, compare what happens before M phase and what happens during M phase

Answer 26

Before M-phase -PP2A is active -PP2A dephosphorylates - M-Cdk targets to stop progression into mitosis During M-phase -M-cyclin is produced -M-Cdk is active -M-Cdk indirectly inhibits PP2A activity - M-cyclin phosphorylates its targets to promote mitosis progression

Question 27

cdk inhibitor proteins (ckis) bind cyclin-cdks and 2 examples

Answer 27

ckis disrupt the cyclin-cdk interaction, which inactivates the cdk (cki like a clamp to block active site and distort atp binding site) examples: p27, p21

Question 28

t/f the inhibitory phosphorylation is at a different site from the activating phosphate added by cak

Answer 28

true

Question 29

what are the functions of wee1 kinase, cdc25 phosphatase

Answer 29

wee1 kinase: adds inhibitory phosphorylation cdc25 phosphatase: can remove the inhibitory phosphorylation

Question 30

which two enzymes have opposite effects in regards to cyclin cdks

Answer 30

wee1 kinase (inhibits) vs cdc25 phosphatase (removes the inhibitory phosphorylation = activates)

Question 31

Cdc25 phosphatase can remove the inhibitory phosphorylation on M-Cdk and must be phosphorylated/dephosphorylated to be active

Answer 31

phosphorylated

Question 32

positive/negative feedback loops ensure robust cyclin cdk activation

Answer 32

positive

Question 33

name an example of active m-cdk activates its activators

Answer 33

cdc25 phosphorylation

Question 34

name 2 examples of active m-cdk inhibiting its inhibitors

Answer 34

- pp2a phosphatase inactivation - wee1 kinase phosphorylation

Question 35

describe wee1 phosphorylation and what is it an example of

Answer 35

its an example of active m-cdk inhibiting its inhibitors. wee1 phosphorylation = inactive = more inhibitory phosphate = more active m-cdk (+ feedback)

Question 36

what type of feedback creates an all or nothing choice to proceed

Answer 36

positive feedback

Question 37

How many of the following statements about the cell cycle are TRUE? * During cell growth, all molecules in the cell are produced together over the same time period. * Different cell cycle stages can be directed by the same Cdks. * Different cell cycle stages can be directed by the same Cyclins. * Active and inactive Cdks can have a phosphate group at the Cdk- activating kinase phosphorylation site. a) 1 b) 2 c) 3 d) 4

Answer 37

B. statement 1 is wrong bc you can make and degrade diff cyclins. statement 4 is wrong bc of inhibitory

Question 38

what are examples of molecular inputs that regulate cyclin-cdk activity

Answer 38

mitogens/growth factors

Question 39

____ is transcription factor req for s-phase gene expression

Answer 39

e2f

Question 40

___ binds and inhibits E2F, this can be inhibited by phosphorylation which allows e2f to continue

Answer 40

rb

Question 41

mitogens trigger production of the cell cycle control protein ____

Answer 41

myc

Question 42

are mitogens ec or ir signaling molecules

Answer 42

ec

Question 43

mitogens activate a signalling pathways including: ? (3)

Answer 43

rtk, ras, map kinase cascade

Question 44

activation of rtk, ras, map kinase cascade leads to upregulation expression of ____

Answer 44

myc

Question 45

myc is a key TF involved in _________ control

Answer 45

cell cycle

Question 46

explain how myc activates g1-cdk which inhibit rb

Answer 46

1. Myc activates G1-cyclin gene expression 2. G1-Cdk phosphorylates Rb 3. Phosphorylated Rb releases E2F 4. E2F activates expression of S-phase genes

Question 47

list 2 examples of positive feedback regarding myc activation

Answer 47

- e2f autoactivation - g1/s-cdk and s-cdk phosphorylation of rb

Question 48

dna damage blocks cell cycle progression via _______ and induces ___ TF activation

Answer 48

cki synthesis, p53

Question 49

p53 activates ____ expression which is a cki that inhibits g1/s-cdk and s cdk

Answer 49

p21

Question 50

what is p21 activation caused by (2 upstream steps)

Answer 50

dna damage induces p53 TF activation where p53 activates p21

Question 51

Which of following will mimic the effects of a Cdk inhibitor? a) Cyclin overexpression b) p27 downregulation c) M-cyclin polyubiquitylation d) Cdc25 phosphatase activity

Answer 51

C. A is wrong bc it's the green light. B, p27 is a ski, down regulate an inhibitor does the opposite. D, green light that removes inhibiting phosphorylation