Cell Cycle Control System

Question 1

What checkpoints exist in the cell cycle?

Answer 1

Interphase:
G1 ‘is envt favorable?’
G2 ‘Is envt favorable? all DNA replicated?
Mitosis: metaphase/anaphase ‘are all chromosomes attached to spindle?’

Question 2

What is a conditional mutation?

Answer 2

Protein does not function under specific conditions (e.g. temperature)

CDC genes

Question 3

With a CDC mutation at high temperature, what would happen?

Answer 3

Mitosis doesn’t work, arresting late in mitosis

Question 4

What is a Flow cytometer? What does it do?

Answer 4

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)

Question 5

what’s the acronym Cdk mean?

Answer 5

Cyclin-dependent kinase.

Amount of cyclins are changing

Cdks are constant

Question 6

What complex causes cell to commit to S phase?

What complex stimulates chromosome duplication?

Answer 6

What complex causes cell to commit to S phase? G1/S-cyclin

What complex stimulates chromosome duplication? S-cyclin

Question 7

What major protein is involved in proteolysis in anaphase promotion?

How does it work?

Answer 7

APC (anaphase promoting complex)

Ubiquitinates S/M cyclins

Ubiquitinates Securin

Question 8

What is securin’s role?

Answer 8

Bind to separase, keeps it inactive

(Separase cleaves cohesin)

Question 9

How is cohesin dissociated in anaphase?

Answer 9

Separase (protease) is normally inhibited by securin

Securin disappears

Separase can now destroy cohesin

Question 10

What are indicators that mitosis has ended?

Answer 10

Decreased Cdk activity

Increased Cdk inhibitor proteins

Decreased cyclin expression

Question 11

What is the general overview of cell cycle control?

Answer 11

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)

Question 12

What does Mad2 do?

Answer 12

Spindle-Assembly Checkpoint (before anaphase)

Binds to kinetochores

Inhibits anaphase-promoting complex, stopping it from degrading securin

Question 13

What different checkpoints exist in the cell cycle?

Answer 13

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

Question 14

What do mitogens do?

Answer 14

They’re extracellular proteins that start cell division

(e.g. lift Cdk suppression)

It’s how cells get out of G1 and into S

Question 15

If DNA gets damaged in G1, how is the cell cycle inhibited?

Answer 15

p53 (activator) gets phosphorylated

Binds to P21 gene

Makes P21, which is an inhibitor protein

P21 blocks Cdks

(mutations associated with cancer)

Question 16

Why is the T-loop important?

What happens to it when cyclins bind?

Answer 16

It sterically blocks Cdks from adding phosphates to things

It gets pulled away by Cyclins

Question 17

What does CAK stand for?

What does it do?

Answer 17

Cyclin-activating kinase.

It adds phosphates to threonines in T-loop.

Completely activates kinases.

Question 18

What protein inactivates cyclin/Cdk during G1-S transition?

Answer 18

P27. Binds to active Cyclin-Cdk and prevents it from phosphorylating anything.

Question 19

What protein inhibits cyclin/Cdks in G2-M?

Answer 19

Wee1 kinase

Question 20

How does Wee1 kinase work to inactivate Cyclin/Cdks during the G2-M transition?

Answer 20

Adds a phosphate group to the Cyclin-Cdk to inactivate

Question 21

What protein removes the phosphate group that Wee1 added?

Answer 21

Cdc25 phosphatase

Question 22

When does Cdc25 phosphatase remove the phosphatases Wee1 kinase added?

Answer 22

G2-M transition. Wee1 kinase works right before mitosis as well.

Question 23

What protein degrades securin to activate separase?

How?

Answer 23

APC/C.

Ubiquitinates it, so that proteolysis happens.

Question 24

Can APC/C function by itself?

What protein does it need?

Answer 24

No. Needs Cdc20, which is a subunit. It attaches and activates APC/C.

(helps it find the right target?)

Question 25

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

Question 26

What protein, activated through the Mitogen pathway, is responsible for increasing transcription of G1 cyclins?

Answer 26

Myc

Question 27

What do G1 Cdks activate to transition into S-phase?

Answer 27

Activate E2F proteins (gene regulatory factors), which are activators binding to a bunch of S-phase promoting genes

Question 28

What proteins normally inhibit E2F, preventing S-phase?

How are they removed from E2F?

Answer 28

Rb proteins

They are phosphorylated by active G1-Cdk complexes

Question 29

What do E2F proteins do?

What do they need to work?

What do they need to propagate?

Answer 29

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

Question 30

What’s the end result of DNA damage? What protein is eventually made after a pathway?

What does it do?

Answer 30

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