Deck 13: Vesicular Traffic, Secretion, and Endocytosis

Question 1

The discovery of green fluorescent protein (GFP)has greatly facilitated living cell experiments because:

A)GFP is green.
B)GFP requires a jellyfish-specific cofactor.
C)GFP sequences may be readily fused to those of other proteins.
D)wild-type GFP folding is adapted to normal seawater temperatures,15-25 °C.

Answer 1

C

Question 2

Given the wild type (normal)yeast on the left and the mutant yeast on the right,identify the defective phenotype for the mutant.

A)entry into the ER
B)fusion of transport vesicles from the ER to the Golgi
C)budding from the Golgi to secretory vesicles
D)fusion of secretory vesicles with the plasma membrane

Answer 2

B

Question 3

How are different coat proteins recruited to different sites within the cell?

Answer 3

There are three known classes of coat proteins: clathrin,COPI,and COPII.Small GTPases recruit each to membranes.Sar1 recruits COPII.Sar1 itself is activated by a guanine nucleotide exchange factor,Sec12,an ER integral membrane protein.ARF recruits both clathrin and COPII.How ARF,or different isoforms of ARF,and guanine nucleotide exchange factor(s)recruit different coat protein/adapters to different sites is not yet known.

Question 4

The presence of clathrin mediates vesicular transport:

A)from ER to cis-Golgi.
B)trans-Golgi to endosome.
C)nuclear membrane to endosome.
D)plasma membrane to trans-Golgi.

Question 5

How are SNARE proteins thought to bring about specific membrane fusion?

Question 6

Proteins that function in the ER will encounter which of the following?

A)enzymatic modification of the ER resident soluble protein to add the KDEL sequence
B)release from KDEL receptor binding in the Golgi due to a pH change
C)anterograde transport in COPII coated vesicles
D)sequestration in the ER by KDEL receptors

Question 7

If Sar1 is inserted into the membrane:

A)it is bound to GTP and recruits COPII coat proteins.
B)it is bound to GDP and recruits COPII coat proteins.
C)it is bound to GTP and recruits cargo.
D)it is not bound to GTP or GDP.

Question 8

What is the role of vesicles in the early stages of the secretory pathway such as ER to Golgi trafficking?

Question 9

How can the direction in which vesicles move in a VSV G-based,cell-free system for transport between Golgi compartments be distinguished?

Question 10

The first step in the secretory pathway that should be inhibited by a non-functional mutant of NSF is:

A)ER to Golgi transport.
B)intra-Golgi transport.
C)trans-Golgi network (TGN)transport to the plasma membrane.
D)trans-Golgi network (TGN)transport to endosomes.

Question 11

COPI coat proteins mediate transport between the Golgi apparatus and other organelles.

A)anterograde
B)enterograde
C)retrograde
D)siderograde

Question 12

Cell-free transport assays:

A)complement genetic approaches to the secretory pathway.
B)often probe for changes in the glycosylation state of transported proteins.
C)provide a means to test the effect of added purified proteins.
D)all of the above

Question 13

Vesicle budding recruits proteins that are needed for subsequent:

A)invagination of the vesicle into the ER lumen.
B)selective vesicle targeting and fusion.
C)shedding of integral membrane proteins into the cytosol.
D)assembly of chromosome folding machinery.

Question 14

Which of the following is a forward transport sorting signal acting at the ER?

A)diacidic amino acid motif within the cytosolic domain
B)KDEL (Lys-Asp-Glu-Leu)C-terminal sequence
C)KKXX (Lys-Lys-X-X)within the cytosolic domain
D)NPXY (Asn-Pro-X-Tyr)within the cytosolic domain

Question 15

Which of the following small GTPases are NOT involved in vesicle budding or docking?

A)ARF
B)rab1
C)ras
D)Sar1p

Question 16

Yeast sec mutations:

A)provide little evidence regarding the mechanism,necessitating other assays or information.
B)invariably affect nonessential genes.
C)affect protein transport into mitochondria but not chloroplasts.
D)all fall into the same complementation class.

Question 17

Soluble and membrane proteins advance through the Golgi complex by:

A)cisternal progression.
B)stable continuities between Golgi cisterna.
C)transient continuities between Golgi cisterna.
D)vesicular transport.

Question 18

Endoglycosidase D is a useful reagent because it allows scientists to distinguish glycosylated proteins that:

A)remain in the cis-Golgi.
B)remain in the trans-Golgi.
C)remain in the ER.
D)get secreted.

Question 19

Why is VSV G protein one of the more useful tools in analyzing membrane trafficking?

Question 20

What phenotype would be observed in a cell containing a nonhydrolyzable form of ATP with respect to the vesicles of the secretory pathway?

A)Secretion of peptides from the cell would be increased.
B)Vesicles would be delivered to incorrect target membranes.
C)Uncoated vesicles would accumulate.
D)Coated vesicles would accumulate.

Question 21

In MDCK cells,which of the following is a sorting signal that allows proteins to be targeted to the apical membrane?

A)GPI
B)HA
C)KDEL
D)all of the above

Question 22

Which portion of a clathrin coat recognizes internalization signals such as Leu-Leu,Asn-Pro-X-Tyr,and Tyr-X-X- in the cytosolic domain of cell-surface endocytic receptors?

Question 23

How are soluble,luminal ER proteins that "leak" out of the ER retrieved to the ER?

Question 24

Which of the following is TRUE about lysosomes?

A)They contain enzymes only capable of breaking down nucleic acids.
B)They are bound by a single membrane but can engulf organelles containing double membranes.
C)Proteins targeted to the lysosome are glycosylated in the ER and a specific mannose is phosphorylated.
D)The final,functional state of lysosomal enzymes contains mannose-6-phosphate.

Question 25

Acidification of endosomes is important in dissociating:

A)cholesterol from LDL.
B)iron from transferrin.
C)transferrin from the transferrin receptor.
D)all of the above

Question 26

Lipoproteins are effective in transporting lipid molecules in an aqueous environment because their surface layer is:

A)hydrophobic.
B)glycosidic.
C)amphipathic.
D)hydrophobic and glycosidic.

Question 27

An important molecule for generating fatty acids in the cell enters via receptor-mediated endocytosis.The complex formed between the receptor on the plasma membrane and the important molecule is stable only at neutral pH.Based on this knowledge,you would predict:

A)a COPII-coated vesicle will be required for import.
B)the important molecule enters the cell via a protein channel.
C)both the molecule and the receptor are degraded to release the molecule from the receptor.
D)the molecule is released from the receptor in the endosome.

Question 28

Describe the types of mutations in the LDL receptor that would cause familial hypercholesterolemia.

Question 29

In hepatocytes,the process by which apically destined proteins travel from the basolateral region across the cell before fusing with the apical membrane is called:

A)exocytosis.
B)transcytosis.
C)endocytosis.
D)none of the above

Question 30

Formation of the late endosome/multivesicular endosome occurs by mechanisms similar to those of:

A)exocytosis of insulin in response to glucose levels in the blood.
B)GCA protein-mediated budding at the trans-Golgi network.
C)retrovirus budding from the plasma membrane.
D)none of the above

Question 31

What is autophagy?

Question 32

The mannose 6-phosphate residue is important,as it is required to target soluble enzymes to the__________.The two enzymes responsible for attaching this residue onto these soluble enzymes reside in the ____________.

A)peroxisome;RER
B)lysosome;cis-Golgi
C)nucleus;medial-Golgi
D)endosome;trans-Golgi

Question 33

The LDL receptor is a receptor for:

A)apolipoprotein B.
B)receptor-mediated endocytosis of LDL.
C)cell signaling via activation of adenylate cyclase.
D)apolipoprotein B and receptor-mediated endocytosis of LDL.

Question 34

The topogenic sequence of transferrin must include:

A)a signal sequence and an internal signal-anchor sequence.
B)an internal signal-anchor sequence with positive charges N-terminal to the SA.
C)an internal signal-anchor sequence with positive charges C-terminal to the SA.
D)alternating signal-anchor sequences with stop-transfer sequences.

Question 35

Protein sorting of anterograde cargo to different destinations within the Golgi complex occurs in the:

A)cis-Golgi.
B)medial-Golgi.
C)trans-Golgi.
D)trans-Golgi network.

Question 36

Professor George Palade's elegant experiment to follow protein synthesis and trafficking,published nearly 60 years ago,provided us with a great deal of information and has been used as a tool by several investigators.If you had access to all the reagents needed to repeat the in vitro experiment,describe what you would need to do to see the progression of newly synthesized proteins and their transport in the cell.

Question 37

The mannose 6-phosphate residue is important,as it is required to target soluble enzymes to the lysosome.The two enzymes responsible for attaching this residue onto these soluble enzymes reside in the:

A)RER.
B)cis-Golgi.
C)medial-Golgi.
D)trans-Golgi.

Question 38

How are clathrin-coated vesicles pinched off?

Question 39

Receptor-mediated endocytosis of iron-carrying transferrin results in:

A)release of iron and proteolysis of the transferrin protein for recycling inside the cell.
B)transferrin/transferrin receptor complexes in the cytosol of the cell.
C)release of iron from the endosome to the cytosol.
D)vesicle formation at the plasma membrane mediated by COP proteins.