Midterm 2 - Notes 4 (Part 3)

Question 1

What does Ras do in its natural form? (2)

Answer 1

1. It helps regulate entry into the S phase

2. Monitor GTPase

Question 2

What is Ras involved with?

Answer 2

Cell cycle control

- entry into the S phase

Question 3

What does Ras encode?

Answer 3

A small GTP binding protein called GTPase

Question 4

What is Ras activated by?

Answer 4

GEF

- turns on

Question 5

GEF

Answer 5

Guanine nucleotide exchange factor

Question 6

What does GEF lead to?

Answer 6

Activation of downstream signalling components

- eg) MAP Kinase

Question 7

What is Ras inactivated by?

Answer 7

GAPs

- turns off

Question 8

GAP

Answer 8

GTPase activating enzyme

- enhance intrinsic GTPase activity

Question 9

What can happen when Ras is mutated?

Answer 9

It can stay active and create mutations

Question 10

What activates Ras?

Answer 10

A mitogen

Question 11

What does Ras initiate?

Answer 11

MAP kinase cascade

Question 12

MAPK

Answer 12

Mitogen activated protein kinase

Question 13

What does Ras activates?

Answer 13

MAP kinase kinase kinase

• phosphorylates MAP kinase kinase
• phosphorylates MAP kinase
• phosphorylates target proteins like TF

Question 14

What is used to help activate proteins?

Answer 14

ATP

Question 15

Can you phosphorylate more then 1 protein?

Answer 15

Yes

Question 16

What do you get through a kinase type cascade?

Answer 16

Strong amplification

Question 17

What does phosphorylation allow?

Answer 17

Cross connection (activation)

Question 18

What are the 6 steps in Ras activation?

Answer 18

1. Ras activated by exchange of GDP for GTP
2. Active Ras recruits, binds and activates Raf
3. GTP hydrolysis leads to dissociation of Ras from Raf
4. Raf activates MEK
5. MEK activates MAPK
6. Dimeric form of MAPK translocates to the nucleus
   - activates many TF

Question 19

In the S-phase activation pathway what does binding of a mitogen to a cell surface receptor lead to?

Answer 19

Activation of a specific GEF which leads to the activation of Ras

Question 20

What does activated Ras initiate?

Answer 20

MAPK cascade

Question 21

What does activated MAPK phosphorylate?

Answer 21

TF

Question 22

What does Myc activates?

Answer 22

Transcription of delayed response genes

Question 23

What is an example of a delayed response gene?

Answer 23

G1/S cyclins

Question 24

What do cyclins bind to?

Answer 24

CDK

Question 25

CDK

Answer 25

Cyclin dependent kinase

Question 26

What complex phosphorylates Rb?

Answer 26

G1/CDK

Question 27

What is p53?

Answer 27

A famous proto oncogene

Question 28

Where is mutated p53 most commonly found?

Answer 28

Many types of cancer

Question 29

Is p53 essential for development?

Answer 29

No | - homozygous null mutations (in a mouse) appear normal

Question 30

What makes amounts of p53 increase?

Answer 30

Stress

Question 31

What are 2 examples of stresses that can increase amount of p53 and cause damage?

Answer 31

1. UV radiation | 2. X-rays

Question 32

What are 4 kinds of signals that come from tumour cells?

Answer 32

1. Hyper-proliferation signals 2. DNA damage 3. Telomere shortening 4. Hypoxia

Question 33

What is a hallmark of tumour formation?

Answer 33

Hypoxia

Question 34

What is p53's primary role?

Answer 34

Prevention of cancer - is a tumour suppressor gene - its a TF

Question 35

Where are most cancerous LOF mutations located?

Answer 35

In DNA binding domains | - when mutated it prevents it to bind to its target gene and acts as a regulatory gene

Question 36

What does DNA damage induce?

Answer 36

Kinase cascade

Question 37

What happens when p53 is phosphorylated?

Answer 37

It gets activated

Question 38

What is produced in high levels?

Answer 38

p53 | - as long as there is no signal that activates the protein we get binding

Question 39

What is one target of p53 transcriptional activation?

Answer 39

p21 protein

Question 40

What does high turn over rate for p53 lead to?

Answer 40

Leads to little p53 present (in a steady state) in the cell because it is degraded very quickly

Question 41

What does p21 bind to?

Answer 41

G1/S phase activated cyclin dependent kinase | - G1/S-CDK

Question 42

What happens when p21 bind to G1/S-CDK?

Answer 42

It inactivates it

Question 43

What does phosphorylation of p53 prevent?

Answer 43

Prevents binding of p53 to Mdm2

Question 44

What happens when p53 is bound to Mdm2?

Answer 44

It is targeted for degradation

Question 45

When is p53 a stable protein?

Answer 45

When it is not bound to Mdm2

Question 46

What happens when Mdm2 is no longer bound to p53?

Answer 46

It is able to proceed with transcription

Question 47

What can p21 engage in?

Answer 47

Protein protein interaction - can bind to CDK - this inactivates it

Question 48

What happens if DNA is damaged?

Answer 48

It cant enter into the S-phase