Homework Assignment #5 (due date Friday, April 24, 5pm)
Last 6 digit SID: 10668240 (22pts)
1) You are tracing the path of a secretory protein from its synthesis to its export from a cell. You
have added radioactive amino acids to a culture of cells, and then measured the amount of
radioactivity that shows up in the proteins of each of the cell fraction. List the order in which
proteins of these fractions first exhibit radioactivity:
I secretory vesicles
II Golgi complex
III rough ER
IV smooth ER
a. III, II, I, out of the cell
b. III, II, IV, V, out of the cell
c. V, III, II, I, out of the cell
d. IV, III, II, I, out of the cell
2) Uptake of low density lipoproteins (LDL) occurs by _____, whereas retrieval of plasma
membrane after extensive secretory activity occurs by ______.
a. receptor mediated endocytosis, bulk phase endocytosis
b. bulk phase endocytosis, receptor mediated endocytosis
c. receptor mediated endocytosis, receptor mediated endocytosis
d. bulk phase endocytosis, bulk phase endocytosis
3) A certain integral protein of the plasma membrane has two transmembrane domains in which
both the C terminus and the N terminus are directed toward the cell exterior in the mature
protein. Where are the C and N termini located when the protein is newly translocated into
the RER membrane? Into the Golgi? Into the secretory vesicles?
The types of proteins that have this quality are from a large family of G –protein coupled receptor which can contain
seven transmembrane a helices.
They are the most abundant type IV-B proteins where the N – terminus extends into
the exoplasmic space.
The N termini when first a helix inserts the nascent chain into the translocoon the N termini