Cell Replication

Question 1

What is the Cell Cycle?

Answer 1

Orderly sequence of events in which the cell duplicates and divides in 2

Question 2

What are the three stages of the cell cycle?

Answer 2

Duplication
Division
Co-ordination

Question 3

Why may different cells divide at different rates?

Answer 3

Adult vs Embryonic cells
Complexity of system
Necessity for renewal
State of differentiation

Question 4

Which phases make up Interphase?

Answer 4

G1
S (DNA replication)
G2

Question 5

What is the M phase?

Answer 5

Mitosis (nuclear division)
Cytokinesis (cytoplasmic division)

Question 6

What is the quiescent phase?

Answer 6

Inactive stage that occurs when cell leaves the cell cycle (after Mitosis). May stay in this phase until it is triggered externally to enter G1.

Question 7

Why might a cell pause during cell cycle?

Answer 7

DNA repair
undergoes apoptosis if mistakes in DNA are too much to repair.

Question 8

What is c-Myc?

Answer 8

Transcription factor-stimulates expression of cell cycle genes.
Oncogene-overexpressed in many tumours.

Question 9

How might cells leave G0?

Answer 9

Response to extracellular growth factors
Signal amplification
Signal integration by other pathways
Ras/Raf/MEK/ERK- increase protein synthesis and decrease protein degradation leading to cell growth

Question 10

What oncogene causes progression of cell from G0 to S phase and how does it do this?

Answer 10

c-Myc
Increases the concentration of Cyclin D

Question 11

What is the purpose of Cdk (cyclin dependent kinases)

Answer 11

Phosphorylation at serine/threonine/tyrosine

Question 12

Where are Cdks found?

Answer 12

All proliferating cells

Question 13

When are Cdks active?

Answer 13

ONLY when bound to cyclin

Question 14

What allows progression into the S phase?

Answer 14

when cyclin 4/6 are bound to cyclin D

Question 15

What is progeny?

Answer 15

Daughter cells that carry genetic defects

Question 16

What effect does phosphorylation have on kinases?

Answer 16

Activates them

Question 17

What effects does phosphatases have on kinases?

Answer 17

Turns them off by dephosphorylation

Question 18

How are Cdks activated?

Answer 18

Cyclin produced and binds to Cdk
Phosphorylation of Cdk-cyclin complex at inhibitory and activating sites of Cdk
Phosphatases remove inhibitory phosphate from Cdk, activating it

Question 19

How does positive feedback act to increase the amount of active Cdk?

Answer 19

Activated Cdk activates more of the phosphatase to remove more inhibitory phosphates from Cdk-cyclin complexes

Question 20

Explain the process by which Cyclins are turned off

Answer 20

Cyclin is ubiquitylated (tagged)
Leading to destruction of cyclin
Therefore Cdk is inactive

Question 21

Which Cyclin-Cdk complex leads to progression into S phase?

Answer 21

Cyclin S- Cdk complex

Question 22

Which Cyclin-Cdk complex leads to progression into the M phase?

Answer 22

Cyclone M- Cdk complex

Question 23

How are specific direction and timing given to the cell cycle?

Answer 23

Cdks become sequentially active and stimulate synthesis of genes required for the next phase

Question 24

How does the activity of the cyclins allow the cell cycle to be cyclical?

Answer 24

Cyclins are susceptible to degradation, so they can be formed again

Question 25

What is Retinoblastoma?

Answer 25

Tumour suppressor

Question 26

How is Retinoblastoma involved in cell proliferation?

Answer 26

Activation of intracellular pathways lead to production of activated Cdk
activated Cdk phosphorylates the Retinoblastoma that is bound to TF, inactivating it
This causes Retinoblastoma to release TF, targeting activation of genes such as DNA polymerase and thymidine kinase

Question 27

What is the function of p53?

Answer 27

They arrest cells with damaged DNA in G1

Question 28

How does p53 act as a tumour suppressor?

Answer 28

When double stranded DNA damage occurs, p53 is not degraded
p53 is activated via phosphorylation
binds to and activates transcription and translation of p21
enzyme formed from expression of p21 inhibits action of Cyclin-cdk complex
Stops cell cycle from continuing