Post-translocational Modifications 2

Question 1

What is the signal for a protein to be sent back to the ER from the Golgi?

Answer 1

A KDEL signal sequence

Question 2

What happens to to protein for it to be sent from the Golgi back to the ER?

Answer 2

In the Golgi, a KDEL receptor acts as transmembrane linked between the KDEL signal sequence and COPI coat on the outside of the Golgi.
Protein sent back to ER.

Question 3

What change is there in pH between the ER and Golgi and why?

Answer 3

ER 7.0
Golgi 6.5
Helps with protein transport

Question 4

How how proteins travel from the Golgi to the lysosomes?

Answer 4

In vesicles

Question 5

What is the signal to send a protein to the lysosomes?

Answer 5

Mannose-6-phosphate

Question 6

What pathway does a protein take to get from the Golgi to the lysosomes?

Answer 6

The addition of a phosphate group to a mannose sugar in the golgi.
This binds to a M6P receptor on the trans Golgi and the protein is taken in a vesicle to the lysosome.
It’s acidic ph removes the phosphate and the receptor is recycled.

Question 7

What is I-cell disease?

Answer 7

Deficiency of a key enzyme (N-acetyl glucosamine phosphotransferase).
Lysosomes become bloated with undegraded material.
An inherited a fatal disease.

Question 8

What is the signal to send a protein to the mitochrondria?

Answer 8

Amphipathetic N-terminal signal (MTS)

Question 9

Explain the pathway a protein takes fro the golgi to the mitochrondria.

Answer 9

Chaperone proteins in the cytoplasm keep the protein unfolded.
Two receptors to pass:
TOM on the outer membrane
TIM on the inner membrane
Once inside target sequence is cleaved, chaperones dissociate and protein can fold.

Question 10

Name a mitochrondrial diseases and how it affects the individual.

Answer 10

Pyruvate Dehydrogenese Defiency
Mutation: Arg to Pro substitution
Proline is a helix breaking amino acid so can destabilise the protein.
Kreb’s cycle cannot occur and there is a lactic acid build up
Neurological problems

Question 11

What is the signal to take a protein to the nucleus?

Answer 11

Nuclear localisation signal (NLS)

Question 12

How is a protein taken from the ER to the nucleus?

Answer 12

A carrier protein importing binds to the protein cargo containing the NLS
It passes through the membrane receptor and inside, Ran-GTP binds to the importin and releases the cargo, which is then recycle in the cytoplasm.

Question 13

Name a disease affecting nuclear protein targeting.

Answer 13

Swyer’s syndrome - loss of NLS determining Y protein - XY genotype but XX phenotype
Keri-Weell dyschodrosteosis - mutation of NLS leading to short stature and lack of skeletal development.