Cell Signalling Week 9 Lectures

Question 1

What is the role of Apaf 1 in the mitochondrial apoptotic pathway?

Answer 1

Association with cytochrome C to stimulate activation of caspases.

Question 2

What form do they exist in?

What is the main role of caspases in the mitochondrial apoptotic pathway?

Answer 2

• Transduction of apoptotic signals from the cell surface or the mitochondria.
• Exist in the cytoplasm as pro-caspases (inactive form).

Question 3

What is the function of Smac/DIABLO in the mitochondrial pathway of apoptosis?

Answer 3

To bind and inhibit the inhibitors of apoptosis (IAPs)

Question 4

What are mesenchymal cells are characterized by?

Answer 4

High motility

Question 5

5 steps

Outline the main steps of apoptosis.

Answer 5

• Cell loses volume and cell membrane starts to bleb and become ruffled.
• Cell and nucleus shrink.
• Chromatin condensation.
• Full condensation of nucleus, eventually breaks up.
• Cell fragments into membrane-bound apoptotic bodies.

Question 6

What are flippases and what is their role?

Answer 6

Proteins that keep phosphatidylserines on inner (cytosolic) leaflet of plasma membrane in steady-state.

Question 7

What are scamblases and what is their role?

Answer 7

Activated by caspase enzymes, externalise phosphatidylserines during apoptosis.

Question 8

How can we use this flipping of phosphatidylserine to detect cells going through apoptosis?

Answer 8

Annexin V is a protein that binds PS.
We can conjugate Annexin V to a fluorescent marker.
Incubate cells with fluorescently conjugated Annexin V will label cells going through apoptosis.

Question 9

What is Propidium Iodide?

Answer 9

A DNA-intercalating dye that can’t penetrate an intact cell membrane.

Question 10

What is necrosis?

Answer 10

• Accidental cell death due to physical damage.
• Cell swells and eventually lyses.
• Unlike apoptosis, this triggers inflammation.

Question 11

What are the 2 molecular mechanisms of apoptosis?

Answer 11

• Mitochondrial pathway (intrinsic)
• Death receptor pathway (extrinsic)

Question 12

What are the ‘pro-apoptosis’ proteins involved in the creation of pores in the mitochondrial membrane?

Answer 12

Bax and BH3-only family proteins cause formation of pores in outer membrane of mitochondria - cytochrome C can leach out.

Question 13

What are the ‘pro-survival’ proteins involved in the creation of pores in the mitochondrial membrane?

Answer 13

BH-2 family proteins block Bax and BH3-only family proteins, preventing them from creating pores in outer mitochondrial membrane.

Question 14

How does the death receptor pathway differ from the mitochondrial pathway?

Answer 14

Caspases are activated by binding of a ligand to extracellular ‘death receptors’.

Question 15

What is meant by the term ‘second messenger’? Give examples of second messengers.

Answer 15

Second messengers are produced by the activation of effector enzymes:
Examples of: cAMP, IP3 and DAG

Question 16

How do receptors stimulate cell growth and division?

Answer 16

Example of EGF
1. Binds on extracellular side causing activation of Tyrosine kinase catalytic domain.
2. Phosphorylation of tyrosine residues.
3. Phosphorylated tyrosine recruits proteins via SH2 to receptor
4. SH2 proteins transmit signal from receptor to nucleus.
5. Induces transcription and cell proliferation in the nucleus.

Question 17

What are potential consequences of mutation in the EGF receptor gene?

Answer 17

• Increased quantity of EGF receptors - more transcription, more cell proliferation. Increased rate of the G phases (S phase cannot be sped up).
• Increased activity of ECF receptor catalytic domain.

Question 18

What is chemotaxis?

Answer 18

The migration of cells towards a specific signal.