Exam 2 questions/concepts

Question 1

If you delete the KDEL sequence from PDI (a soluble lumenal protein in the ER), where, in
addition to the ER, will you most likely find the mutant protein?

Answer 1

Extracellular Space

Question 2

ER is the site for the folding and modification of proteins in all of the following, except
_________.

Answer 2

Golgi, Endosome, PM, lysosome, EXCEPT Mitochondria

Question 3

Insulin is a protein hormone secreted by the pancreas. What two sorting signals does insulin
likely possess?

Answer 3

ER export signal; ER-targeting signal sequence

Question 4

Where is KDEL located and functional?

Answer 4

ONLY in the the lumen and at C-terminus (extracellular space).

Question 5

What organelles are a part of the endomembrane system?

Answer 5

ER, golgi, endosome, lysosome, plasma membrane

Question 6

How can you convert a soluble ER lumenal protein into a type I transmembrane protein?

Answer 6

Adding a stretch of 20 hydrophobic amino acids.

Question 7

How do Rabs mediate vesicle fusion?

Answer 7

Rabs bind GTP and recruit tethering molecules for vesicle docking with target membrane.

Question 8

How do SNAREs mediate vesicle fusion?

Answer 8

v- and t-SNAREs form trans-SNARE complexes to drive vesicle docking and fusion by forcing the membranes together.

Question 9

Cisternal Maturation model, how are proteins destined for secretion transported through the Golgi?

Answer 9

Cisternae progressively mature in the cis-medial-trans direction, carrying cargo along with them.

Question 10

How are Golgi resident proteins retained?

Answer 10

By retrograde transport in COP I vesicles.

Question 11

Where are EGF receptors normally localized and degraded?

Answer 11

Localized on PM. Degraded in lysosome. (transmembrane protein)

Question 12

What is PERK and where is it degraded?

Answer 12

ER-bound transmembrane protein. Degraded in cytosol by proteasomes.

Question 13

What molecule is used to conjugate EGF and PERK prior to degradation and what is different between the two?

Answer 13

Ubiquitin.

1. EGF receptor: single ubiquitin
2. PERK: ubiquitin chain

Question 14

If you use a small molecule drug to inactivate Sec12, what will most likely happen?

Answer 14

Sar1 fails to associate with the ER.

Question 15

Tunicamycin is a small molecule that blocks N-linked glycosylation. If you treat cells with
tunicamycin, what biological process will be directly affected?

Answer 15

Calnexin binding to substrate (calreticulin involved too).

Question 16

BiP belongs to the HSP70 chaperone family. It contains a C-terminal KDEL sequence. BiP is
thought to play important roles in retaining proteins in the ER and preventing the secretion of
unfolded/misfolded proteins from the cell. Explain how BiP may perform this function.
Hint: Make sure to include the role of pH in your answer.

Answer 16

1. BiP binds to hydrophobic stretches of misfolded/unfolded proteins and retrieves them from the cis-Golgi.
2. KDEL receptor recognizes BiPs KDEL sequence at the slightly lower pH of the cis-Golgi and retrieves BiP and the associated unfolded/misfolded protein back to the ER. In the ER, at the higher pH, BiP dissociates from the KDEL receptor.

Question 17

What is the charge of the cytosolic side?

Answer 17

Negative

Question 18

What is the charge of the lumenal side?

Answer 18

Positive

Question 19

The transport of cargo from the trans-Golgi network to the lysosome is mediated by _______.

Answer 19

Clathrin-coated vesicles

Question 20

Which event does NOT occur within the lumen of an organelle?

Answer 20

Recognition of the N-terminal signal sequence of BiP.

Question 21

Briefly describe the role of RanGTP in nuclear import and export

Answer 21

1. Import: In the nucleus, RanGTP interacts with receptor-cargo complex and the complex dissociates.
2. Export: RanGTP binds Importin-β in the nucleus, as they exit the nucleus, GTP is hydrolyzed to GDP and RanGDP dissociates from Importin-β in the cytoplasm.

Question 22

What does importin-alpha do?

Answer 22

Recognizes the nuclear localization signal (NLS) of a protein targeted for nuclear import.

Question 23

What does importin-beta do?

Answer 23

Recognizes RanGTP.