Intracellular Traffic, Sorting of Proteins and Signal transduction

Question 1

This is the targeting sequence for luminal ER

a. NLS
b. PTS
c. KDEL
d. Mannose 6-phosphate

Answer 1

C. KDEL

Carboxyl-terminal KDEL sequence (Lys-Asp-GLu-Leu) in ER-resident proteins in COPI vesicles

Question 2

The vesicle involved in anterograde transport of protein synthesized in membrane bound polyribosome

a. Secretory vesicle
b. COP I
c. Clathrin
d. COP II

Answer 2

D. COP II

COP II vehicles carry proteins that are transported out of the ER to the cis-Golgi (anterograde transport)

Clathrin-coated vesicles are involved in endocytosis, carrying cargo to late endosomes and to lysosomes

Mannose-6-phosphate acts as a signal for transporting enzymes to lysosomes

COP I vehicles transport protein from GA to the ER (retrograde transport) and may be involved in some intra-Golgi transport

Question 3

True about mitochondrial protein translocation, EXCEPT:

a. The process occurs posttranscriptionally
b. The protein is in folded state during the process
c. Proton motive force is used during import
d. Chaperone is required

Answer 3

B is wrong since protein must be in unfolded state to pass through the complexes (made possible by ATP-dependent binding to several chaperone proteins including Hsp70)

A is correct since Mitochondrial protein translocation occurs posttranslationally, after the proteins are released form the cytosolic polyribosmes
C is correct since proton-motive force across the inner membrane is required for import; it is made up of the electric potential across the membrane (inside negative) and the pH gradient
D is correct since in mitochondria, chaperones are involved in translocation, sorting, folding, assembly, and degradation of imported proteins

Question 4

The amino acid in the target protein that conjugates with E2 during ubiquitination:

a. Arg
b. Lys
c. His
d. Val

Answer 4

B. Lysine

E3: Ligase enzyme catalyzes transfer of ubiquitin from E2 to an epsilon-amino group on a LYSINE of the target protein

Question 5

A hormone that inhibits adenylyl cyclase activity

a. TSH
b. Glucagon
c. Acetylcholine
d. Calcitonin

Answer 5

C. Acetylcholine

Hormones that inhibit Adenylyl cyclase (Hi):
Acetylcholine
alpha2-adrenergic
Angiotensin II
Somatostatin

Question 6

All of the following stimulate adenylyl cyclase except:
A. ACTH
B. ADH
C. beta-adrenergics
D. alpha-adrenergics
E. NOTA

Answer 6

D. alpha-adrenergics (inhibitor)

Hormones that stimulate Adenylyl Cyclase:

• ACTH
• ADH
• beta-Adrenergics
• Calcitonin
• CRH
• FSH
• Glucagon
• hCG
• LH
• LPH
• MSH
• PTH
• TSH