L8-Trafficking, organelles and diseases

Question 1

1. What are the symptons of CF caused by?
2. What does it lead to?

Answer 1

1. The inability of certain cells to transport chloride ions out of the cell. (mucuous build up, infection)
2. Respiratory problems and can lead to liver and pancreas failure.

Question 2

Whats the most common mutation for cystic fibrosis?

Answer 2

ΔF508

(ΔPhe508)

Question 3

Why is CF an ER storage disease?

Answer 3

Proteins accumulate in the ER when they’re made. There’s a defect in trafficking proteins to the plasma membrane.

Question 4

Give examples of ER storage diseases

Answer 4

1. Cystic fibrosis
2. Retinis pigmentosa (night blindness)

Question 5

In ER storage diseases, why can’t they leave the ER?

Answer 5

The defective genes cause mutant proteins which fail the ER quality control step.

Question 6

What are the ER quality control steps?

Answer 6

1. Recognition (of misfolded protein)
2. Retention
3. Removal

Question 7

What do chaperones do?

Answer 7

Help proteins to fold correctly and prevent them from aggregating.

Question 8

What do chaperones do when the CFTR protein is misfolded?

Answer 8

Usually they bind transiently to normal CFTR (in the ER lumen and cytosol) and help it fold.

Chaperones bind to mutant proteins but don’t let go.

Question 9

What causes mutant proteins to be recognised as misfolded?

Answer 9

The prolonged interaction of chaperones

Question 10

What can the accumulation of misfolded proteins in the ER trigger?

What happens if this isn’t effective?

Answer 10

UPR- unfolded protein response.

The signalling pathway programmes the cell to make more ER chaperones and expand the ER to restore balance.

If UPR doesn’t restore balance- cells may die via apoptosis.

Question 11

What does the specific and regulated degradation fo cytosolic proteins depend on?

Answer 11

Upon the attachment of polymers of a small protein- Ubiquitin.

Question 12

What targets proteins for destruction?

Answer 12

The attachment of multiubiquitin chains

Question 13

What are ubiquinated proteins degraded by?

Answer 13

Proteosomes. These are large protein complexes with a central cavity where proteins are converted to short peptides. (using ATP).

Question 14

What is ERAD?

Answer 14

ER associated degradation.

(misfolded proteins retained in the ER eventually being degraded)

Question 15

Does ERAD just happen in the ER?

Answer 15

No. The final stages are cytosolic

Question 16

What is ER retained CFTR destroyed by?

Answer 16

The proteosome

Question 17

Where can recognition occur in ERAD?

Answer 17

ER lumen, ER membrane or cytosol

Question 18

What ubiquitates defective proteins?

Answer 18

specialised components of the ER membrane

Question 19

What happens to misfolded proteins recognised in the ER?

Answer 19

There are no proteosomes inside the ER. So they’re retranslocated from the ER back into the cytosol.

Question 20

What’s a potential therapy for CF involving chaperones?

Answer 20

Manipulate the ER quality control. Get the chaperones to release the Δf508 from the ER. (as it’s partially functional).

?is this right

Question 21

What characterizes Alzheimer’s disease?

Answer 21

Insoluble plaques with lots of protein-beta-amyloid

Aβ

Question 22

How is Aβ produced?

Answer 22

Made from the amyloid precursor protein (APP).

This is a single-spanning membrane protein. (made at the ER and delivered to the cell surface)

After synthesis APP can be proteolytically cleaved by enzymes to make smaller fragements.- including Aβ.

Question 23

Once at the cell surface APP can be processed by two pathways. What are they and which is harmful?

Answer 23

1. Cleavage by α-secretase then γ-secretase.
   Makes- P3. Which is short and NOT HARMFUL.
2. Cleavage by β-secretase then γ-secretase.
   Makes-**Aβ peptide. **Which is longer and HARMFUL.
   Amyloidogenic.

Question 24

What is made in each pathway of APP cleavage and which is amyloidogenic?

Answer 24

1. alpha- makes P3. Not amyloidogenic.
2. beta- makes Aβ peptide- Amyloidogenic , bad.

Question 25

Which protein is particularly harmful in Alzheimer’s? Why?

Answer 25

Aβ peptides of 42 residues.
They have a strong tendency to form plaques.

Question 26

What other factors are linked to AD?

Answer 26

1. Apolipoprotein E (E4 allele).
   A gene encoding a cholesterol transport protein.
2. Tau- a microtubule associate protein. Tau filaments linked to AD.