Cell Cycle Control System Flashcards
What checkpoints exist in the cell cycle?
Interphase:
G1 ‘is envt favorable?’
G2 ‘Is envt favorable? all DNA replicated?
Mitosis: metaphase/anaphase ‘are all chromosomes attached to spindle?’
What is a conditional mutation?
Protein does not function under specific conditions (e.g. temperature)
CDC genes
With a CDC mutation at high temperature, what would happen?
Mitosis doesn’t work, arresting late in mitosis
What is a Flow cytometer? What does it do?
Analyze DNA content with fluorescent binds
Analyze a ton of cells at once
Separate cells that are different from each other (e.g. ones with fluorescent protein)
what’s the acronym Cdk mean?
Cyclin-dependent kinase.
Amount of cyclins are changing
Cdks are constant
What complex causes cell to commit to S phase?
What complex stimulates chromosome duplication?
What complex causes cell to commit to S phase? G1/S-cyclin
What complex stimulates chromosome duplication? S-cyclin
What major protein is involved in proteolysis in anaphase promotion?
How does it work?
APC (anaphase promoting complex)
Ubiquitinates S/M cyclins
Ubiquitinates Securin
What is securin’s role?
Bind to separase, keeps it inactive
(Separase cleaves cohesin)
How is cohesin dissociated in anaphase?
Separase (protease) is normally inhibited by securin
Securin disappears
Separase can now destroy cohesin
What are indicators that mitosis has ended?
Decreased Cdk activity
Increased Cdk inhibitor proteins
Decreased cyclin expression
What is the general overview of cell cycle control?
G1-Cdk > s-cyclin + g1/s-cyclin synthesis
G1/S-Cdk > S-Cdk causes DNA replication
S Phase
M-Cdk starts mitosis
APC/C to get through anaphase
(Low Cdk triggers G1)
What does Mad2 do?
Spindle-Assembly Checkpoint (before anaphase)
Binds to kinetochores
Inhibits anaphase-promoting complex, stopping it from degrading securin
What different checkpoints exist in the cell cycle?
G1-S
Intra-S phase
DNA-damage checkpoint (G1)
DNA-damage checkpoint 2 (S-phase)
DNA damage checkpoint 3 (right before G2)
G2-M
DNA damage
Pre-anaphase
Spindle-assembly checkpoint
Spindle-position checkpoint
What do mitogens do?
They’re extracellular proteins that start cell division
(e.g. lift Cdk suppression)
It’s how cells get out of G1 and into S
If DNA gets damaged in G1, how is the cell cycle inhibited?
p53 (activator) gets phosphorylated
Binds to P21 gene
Makes P21, which is an inhibitor protein
P21 blocks Cdks
(mutations associated with cancer)
Why is the T-loop important?
What happens to it when cyclins bind?
It sterically blocks Cdks from adding phosphates to things
It gets pulled away by Cyclins
What does CAK stand for?
What does it do?
Cyclin-activating kinase.
It adds phosphates to threonines in T-loop.
Completely activates kinases.
What protein inactivates cyclin/Cdk during G1-S transition?
P27. Binds to active Cyclin-Cdk and prevents it from phosphorylating anything.
What protein inhibits cyclin/Cdks in G2-M?
Wee1 kinase
How does Wee1 kinase work to inactivate Cyclin/Cdks during the G2-M transition?
Adds a phosphate group to the Cyclin-Cdk to inactivate
What protein removes the phosphate group that Wee1 added?
Cdc25 phosphatase
When does Cdc25 phosphatase remove the phosphatases Wee1 kinase added?
G2-M transition. Wee1 kinase works right before mitosis as well.
What protein degrades securin to activate separase?
How?
APC/C.
Ubiquitinates it, so that proteolysis happens.
Can APC/C function by itself?
What protein does it need?
No. Needs Cdc20, which is a subunit. It attaches and activates APC/C.
(helps it find the right target?)
Yeast can go through mitosis normally without securin
But you have mutant yeast that can’t degrade securin, they can’t activate separase and enter anaphase
Cells without Cdc 20 also can’t enter anaphase
Cells with neither securin or Cdc20 can’t exit anaphase (they can separate chromatids, can’t do anything else)
So, in wild-type cells:
A) Degradation of securin is necessary to trigger sister chromatid separation
B) Cdc20-APC/C is NOT necessary for sister chromatid separation
C) Cdc20-APC/C is NOT necessary for later events in anaphase
D) all of the above
What protein, activated through the Mitogen pathway, is responsible for increasing transcription of G1 cyclins?
Myc
What do G1 Cdks activate to transition into S-phase?
Activate E2F proteins (gene regulatory factors), which are activators binding to a bunch of S-phase promoting genes
What proteins normally inhibit E2F, preventing S-phase?
How are they removed from E2F?
Rb proteins
They are phosphorylated by active G1-Cdk complexes
What do E2F proteins do?
What do they need to work?
What do they need to propagate?
They are activators that bind to genes required for S-phase entry
They need to not have Rb on them to be activated
They can also activate themselves - E2Fs bind to their own target genes and self-propagate
What’s the end result of DNA damage? What protein is eventually made after a pathway?
What does it do?
P21, made after some intermediary steps
It binds to G1/S-Cdk and inactivates them, preventing them from dissociating Rb proteins from E2F, and blocking S-phase
