Lecture 19: Cell cycle

Question 1

What two processes must be aligned for cell division to occur?

Answer 1

Chromosome division and cell division

Question 2

What is the structure of the embryonic cell cycle?

Answer 2

S and straight to M

Question 3

What is the structure of the somatic cell cycle?

Answer 3

Alternating S and M phases
Separated by gap phases

Question 4

What are the two steps needed for cell division to occur?

Answer 4

Nuclear division
Cytoplasm division

Question 5

What needs to happen for a cell to enter mitosis?

Answer 5

All DNA is replicated
All DNA is damage repaired

Question 6

What needs to happen for a cell to enter S phase?

Answer 6

Growth stimulatory signals are present
Anti-proliferative signals are absent
Sufficient nutrients

Question 7

What drives the cell cycle engine?

Answer 7

Cdk-Cyclin complex

Question 8

What cyclin and cdk is involved in G1?

Answer 8

Cyclin D
Cdk 4 and 6

Question 9

What cyclin and cdk is involved in G1/S?

Answer 9

Cyclin E
Cdk 2

Question 10

What cyclin and cdk is involved in S?

Answer 10

Cyclin A
Cdk 2

Question 11

What cyclin and cdk is involved in M?

Answer 11

Cyclin B
Cdk 1

Question 12

Do cdk levels stay constant or change during the cell cycle?

Answer 12

Constant

Question 13

Do cyclin levels stay constant or change during the cell cycle?

Answer 13

Rise and fall

Question 14

How is cdk activated?

Answer 14

1. Cyclin binds to Cdk
2. Conformational change pulls T loop away from Cdk active site
3. Substrate can bind

Question 15

What are the four different ways of regulating cyclin-cdk complexes?

Answer 15

Phosphorylation
Ubiquitin-mediated proteolysis
Binding of CKI
Localisation

Question 16

What is the effect of phosphorylation regulation?

Answer 16

Can be inhibitory or activating

Question 17

What is the effect of regulation by ubiquitin mediated proteolysis?

Answer 17

Breaks down cyclin
Provides directionality

Question 18

What is the effect of regulation by binding of CKI?

Answer 18

Cdk inhibitors are unregulated due to damage

Question 19

What is the effect of regulation by localisation?

Answer 19

Cyclin B is imported to nucleus before mitotic

Question 20

What is the function of checkpoints?

Answer 20

Ensure cell cycle and chromosome cycle are coupled

Question 21

What is the overall process of getting in and out of mitosis?

Answer 21

1. Switch off DNA damage checkpoints
2. Activate Cdk1 to get into mitosis
3. Silence spindle assembly checkpoint
4. Inactivate Cdk1 to get out of mitosis

Question 22

What is the process of step 1 getting into mitosis?

Answer 22

1. Signalling pathways block Cdk1 activation
2. Override G2/M checkpoint

Question 23

What is the process of step 2 getting into mitosis?

Answer 23

1. Cdk1 activation
2. Phosphorylation of target proteins including other kinases
3. Activates mitotic pathways and inactivates interphase pathways
4. Brings about the morphological changes associated with mitosis

Question 24

What is the process of step 3 turning off mitosis?

Answer 24

1. APC is active in mitosis
2. When all kinetochores attached SAC is silenced and APC is activatd
3. Cyclin B is degraded
4. Mitotic exit
5. Securin degraded by APC
6. Sister chromatid separation

Question 25

What is the full overall process of turning mitosis off and on?

Answer 25

1. DNA damage activates Wee1 to put inhibitory phosphates on Cdk1
2. Cdc25 removes inhibitory phosphates leading to Cdk1 activation
3. When all kinetochores are attached to spindle the APC is activated
4. Cyclin B is ubiquitinated and degraded and Cdk1 is inactivated