Exam 2 questions/concepts Flashcards Preview

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Flashcards in Exam 2 questions/concepts Deck (23):

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?

Extracellular Space


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

Golgi, Endosome, PM, lysosome, EXCEPT Mitochondria


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

ER export signal; ER-targeting signal sequence


Where is KDEL located and functional?

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


What organelles are a part of the endomembrane system?

ER, golgi, endosome, lysosome, plasma membrane


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

Adding a stretch of 20 hydrophobic amino acids.


How do Rabs mediate vesicle fusion?

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


How do SNAREs mediate vesicle fusion?

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


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

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


How are Golgi resident proteins retained?

By retrograde transport in COP I vesicles.


Where are EGF receptors normally localized and degraded?

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


What is PERK and where is it degraded?

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


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

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


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

Sar1 fails to associate with the ER.


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

Calnexin binding to substrate (calreticulin involved too).


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.

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.


What is the charge of the cytosolic side?



What is the charge of the lumenal side?



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

Clathrin-coated vesicles


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

Recognition of the N-terminal signal sequence of BiP.


Briefly describe the role of RanGTP in nuclear import and export

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.


What does importin-alpha do?

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


What does importin-beta do?

Recognizes RanGTP.