Tumour Supressor Genes

Question 1

What happens when Ras is mutated?

Answer 1

It’s permanently active stimulating signalling cascade

Question 2

Is the mutation of ras dominant or recessive?

Answer 2

Dominant

Question 3

Are tumour suppressor mutations dominant or recessive?

Answer 3

Recessive

Question 4

What is a diploid cell?

Answer 4

Two copies of each chromosome so having one mutate is enough to maintain humour suppressor gene

Question 5

What do tumour suppressor genes do?

Answer 5

Inhibit cell division

Question 6

What was the first tumour suppressor gene identified?

Answer 6

Retinoblastoma protein

Question 7

What are the two forms of retinoblastoma?

Answer 7

Familial (children)

Sporadic (adults))

Question 8

Is the condition of retinoblastoma recessive or dominant?

Answer 8

Recessive

Question 9

What is retinoblastoma caused by?

Answer 9

Inherited and somatic mutation

Mitotic recombination

Question 10

Why does retinoblastoma inhibit?

Answer 10

G1-S transition

There’s a loss of G1 checkpoint

Question 11

What is the role of p53?

Answer 11

Protect the cell against damaged DNA

Question 12

Why is it called p53?

Answer 12

Size of protein is 53KDa

Question 13

What is the role of P53?

Answer 13

Recognised genetic damage, metabolic stress

It’s a transcription factor

Question 14

When is P53 stabilised?

Answer 14

Presence of genetic damage or cellular stress

Question 15

If DNA is too severe what happens?

Answer 15

Senescence or death (apoptosis)

Question 16

Explain the process of activating p53

Answer 16

DNA is damaged

Signal is passed to p53 via a cascade of protein kinases each phosphorylating and activating each other

Activated p53 is a transcription factor which triggers expression of protein which inhibit cell cycle

Question 17

How does p53 alter gene expression using p21?

Answer 17

Expression regulated by p53
P22 is inhibitor of Cyclin E-Cdk2
Prevents G1 exit causing call to arrest

Question 18

How does p53 alter gene expression by DNA repair proteins?

Answer 18

Expression regulated by p53
Allows cell to repair DNA during cell cycle arrest
If DNA is damage isnt repaired cells enter senescence or apoptosis

Question 19

Define apoptosis

Answer 19

A form of cell death in which programmed sequence oh events leads to the elimination of cells without releasing harmful substances

Question 20

How does apoptosis work?

Answer 20

Normal cell deluded that DNA is beyond repair and so p53 activates apoptosis

Cell shrinks and invagination form at cell surface

Question 21

What factors induce apoptosis?

Answer 21

Signal within cell (Intrinsic apoptosis)
Activation of FAS death receptor (extrinsic apoptosis)

(Both regulated by p53)

Question 22

How is intrinsic apoptosis regulated by p53?

Answer 22

DNA is damaged p53 induces Bid expression
Activated Bid induces Bax to form a pore in the mitochondrial membrane
Release of cytochrome c activates caspases presenting cytoplasm og cell leading to apoptosis

Question 23

How is extrinsic apoptosis regulated by p53?

Answer 23

Activation of p53 induces expression of death receptors
Death receptors are activated by cells expressing Fas ligand eg lymphocytes
Fas ligand activates Fas death receptor and recruits FADD
Formation of the DISC activates caspases that regulate cellular disintegration (apoptosis)