2.10: The Cell Cycle Flashcards
does DNA replication occur in mitosis
NO, before
which two processes are included in M phase
mitosis and cytokinesis
which are the transition to enter mitosis and which questions are asked
G2/M transition
is all DNA replicated? is the environment favorable?
state the purpose of cell cycle checkpoints
ensure conditions are suitable for division
which are the transition to trigger anaphase and proceed to cytokinesis and which questions are asked
metaphase to anaphase transition. are all chromosomes attached to the spindle?
which are the transition to enter cell cycle and proceed to S phase and which questions are asked
start transition. is the environment favorable
at a molecular level, what are checkpoints mediated
the controlled activity of cyclin dependent kinases (Cdks)
what do Cdks do and what do they require
Cdks phosphorylate targets proteins for the cell cycle to progress, Cdks require cyclins to be active
t/f Cdks and cyclins can be present throughout all cell cycle stages
false. Cdks can, cyclins are made and broken down at different cell cycle stages
the cyclin-cdk combo controls what
which target proteins are phosphorylated
S cdk phosphorylates ? at ? stage of the cell cycle
S cdk phosphorylates dna helicases at G1 to S stage of the cell cycle
which cdk complex is is at the start of the cell cycle
G1/S cdk w G1/S cyclin
Mcdk phosphorylates ? at ? stage of the cell cycle
phosphorylates lamin (nuclear envelope breakdown) and microtubule associated proteins (spindle assembly) it is in between the G2 and M
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)
true
for budding yeast, what are the cdk partner(s)
for vertebrates, what are the cdk partner(s)
yeast: cdk1. vertebrates: cdk2
cyclins can be ubiquitinated, polyubiquitination marks cyclins for ________ by the _________
cyclins can be ubiquitinated, polyubiquitination marks cyclins for degradation by the proteasome
if cyclins are broken down, cdks will still/no longer be active
no longer
t/f if cyclins are degraded, cdks are spared
yes
______ & _______ promote M-cyclin degradation
APC/C and Cdc20
APC/C and Cdc20 act as an ?
E3 ubiquitin ligase
which processes determines which cyclin-cdk complex is active at any time
synthesis and degradation
cdks are activated by which enzyme
cdk activating kinase (CAK)
cyclin is absolute required for cdk activity by exposing the _____, once it is exposed, cak can phosphorylate cdk to further activate it
t loop
which enzyme reverse the effects of cyclin cdks by removing phosphorylation from proteins
protein phosphatases (PP2As)
t/f pp2as usually have the same targets as cyclin-cdks
true - pp2a and m-cdk participate in a complex feedback loop
m-cdk and pp2a compete for the same targets, compare what happens before M phase and what happens during M phase
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
cdk inhibitor proteins (ckis) bind cyclin-cdks and 2 examples
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
t/f the inhibitory phosphorylation is at a different site from the activating phosphate added by cak
true
what are the functions of wee1 kinase, cdc25 phosphatase
wee1 kinase: adds inhibitory phosphorylation
cdc25 phosphatase: can remove the inhibitory phosphorylation
which two enzymes have opposite effects in regards to cyclin cdks
wee1 kinase (inhibits) vs cdc25 phosphatase (removes the inhibitory phosphorylation = activates)
Cdc25 phosphatase can remove the inhibitory phosphorylation on M-Cdk and must be phosphorylated/dephosphorylated to be active
phosphorylated
positive/negative feedback loops ensure robust cyclin cdk activation
positive
name an example of active m-cdk activates its activators
cdc25 phosphorylation
name 2 examples of active m-cdk inhibiting its inhibitors
- pp2a phosphatase inactivation
- wee1 kinase phosphorylation
describe wee1 phosphorylation and what is it an example of
its an example of active m-cdk inhibiting its inhibitors. wee1 phosphorylation = inactive = more inhibitory phosphate = more active m-cdk (+ feedback)
what type of feedback creates an all or nothing choice to proceed
positive feedback
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
B.
statement 1 is wrong bc you can make and degrade diff cyclins. statement 4 is wrong bc of inhibitory
what are examples of molecular inputs that regulate cyclin-cdk activity
mitogens/growth factors
____ is transcription factor req for s-phase gene expression
e2f
___ binds and inhibits E2F, this can be inhibited by phosphorylation which allows e2f to continue
rb
mitogens trigger production of the cell cycle control protein ____
myc
are mitogens ec or ir signaling molecules
ec
mitogens activate a signalling pathways including: ? (3)
rtk, ras, map kinase cascade
activation of rtk, ras, map kinase cascade leads to upregulation expression of ____
myc
myc is a key TF involved in _________ control
cell cycle
explain how myc activates g1-cdk which inhibit rb
- Myc activates G1-cyclin gene expression
- G1-Cdk phosphorylates Rb
- Phosphorylated Rb releases E2F
- E2F activates expression of S-phase genes
list 2 examples of positive feedback regarding myc activation
- e2f autoactivation
- g1/s-cdk and s-cdk phosphorylation of rb
dna damage blocks cell cycle progression via _______ and induces ___ TF activation
cki synthesis, p53
p53 activates ____ expression which is a cki that inhibits g1/s-cdk and s cdk
p21
what is p21 activation caused by (2 upstream steps)
dna damage induces p53 TF activation where p53 activates p21
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
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
