Mechanisms of Disease II: Cell Damage and Cell Death part 2

Question 1

What are the microscopic appearances of apoptosis?

Answer 1

Nuclear Changes
• Nuclear chromatin condenses on nuclear membrane.
• DNA cleavage.
Cytoplasmic Changes
• Shrinkage of cell. Organelles packaged into membrane vesicles.
• Cell fragmentation. Membrane bound vesicles bud off.
• Phagocytosis of cell fragments by macrophage and adjacent cell.
• No leakage of cytosolic components.

Biochemical changes
• Expression of charged sugar molecules on outer surface of cell membranes (recognised by macrophages to enhance phagocytosis)
• Protein cleavage by proteases, caspases

Question 2

Read over the different types of substrates and there functions

Answer 2

On document

Question 3

How do we activate the initiator caspases?

Answer 3

• By induced proximity.
• For example:
• In response to receptor dimerization upon ligand binding
OR
• Cytochrome C release from the mitochondria

Question 4

Describe Ligand-induced dimerisation

Answer 4

• Receptor is on the membrane.
• Inside the cell there is the death domain and outside the cell there is the ligand binding domain.
• The receptor recruits an adaptor protein which makes dimers with the death domain however, it also brings inactive procaspase-8 with it.

Question 5

Describe the TNF pathway

Answer 5

• Death inducing signalling complex
• These cells receive death ligand, in this case TNF.
• TNF brings together several receptors for itself which come together on the death adaptor protein.
• The death adaptor protein brings a lot of Procaspase-8 in close proximity.
• As a result of the close proximity, there is autoproteolysis of the procaspase 8.
• The outcome of this is that you have ACTIVE procaspase-8

Question 6

What is cytochrome c?

Answer 6

• Mitochondrial matrix protein
• Known for many years to be released in response to oxidative stress by a “permeability transition”
• Any inducers of the permeability transition also eventually induce apoptosis.

Question 7

Describe the cytochrome c pathway

Answer 7

• Cytochrome C has binding sites on this molecule called APAF.
• APAF has a domain which can bind and recruit caspases (in this case it is caspase 9).
• A few cytochrome C molecules can bring together a few APAF molecules which in turn brings together a few inactive Procaspase-9 molecules.
• Due to the close proximity, you get autoproteolysis, and the procaspase-9 becomes activated.

Question 8

How is the release of cytochrome c regulated?

Answer 8

On document