Question 1

Which of the following best describes the role of the KDEL sequence in protein trafficking within the endomembrane system?

Accepted Answer

It is a retrieval tag that ensures ER-resident proteins are returned from the Golgi to the ER.

Question 2

A mutation in the gene encoding Sar1 would most directly affect which cellular process?

Accepted Answer

Anterograde transport from the ER to the Golgi

Question 3

Which of the following is TRUE regarding the insertion of a Type I transmembrane protein into the ER membrane?

Accepted Answer

A stop-transfer sequence halts translocation, anchoring the protein in the membrane.

Question 4

Which of the following best explains why vesicles have distinctive coats such as clathrin, COPI, and COPII?

Accepted Answer

To maintain compartmentalization of distinct organelle functions.

Question 5

A cell line with a defective COPII protein would most likely accumulate excess proteins in which organelle?

Accepted Answer

Endoplasmic reticulum (ER)

Question 6

Which of the following steps is NOT part of the process of receptor-mediated endocytosis?

Accepted Answer

Direct fusion of the vesicle with the lysosome without uncoating

Question 7

Which of the following is a function of peroxisomes that distinguishes them from lysosomes?

Accepted Answer

Degradation of hydrogen peroxide via catalase

Question 8

Which of the following best describes the role of Rab GTPases in vesicle trafficking?

Accepted Answer

They promote the association of v-SNAREs and t-SNAREs for membrane fusion.

Question 9

A patient is diagnosed with Tay-Sachs disease, a lysosomal storage disorder. Which of the following best explains the cellular defect?

Accepted Answer

Defective acid hydrolase leads to accumulation of gangliosides in neurons.

Question 10

Which of the following is a key difference between constitutive and regulated secretion?

Accepted Answer

Regulated secretion involves vesicles that accumulate and fuse with the plasma membrane only in response to a signal.

Question 11

Which of the following best describes the function of the mannose-6-phosphate tag?

Accepted Answer

It targets soluble lysosomal enzymes to lysosomes via binding to specific receptors.

Question 12

Which of the following statements about SNARE proteins is CORRECT?

Accepted Answer

v-SNAREs and t-SNAREs interact to promote vesicle and target membrane fusion.

Question 13

Which of the following is a direct consequence of a defective V-ATPase in the lysosomal membrane?

Accepted Answer

Lysosomal pH remains neutral, preventing activation of acid hydrolases.

Question 14

Which of the following best explains why the thickness of cellular membranes increases from the ER to the plasma membrane?

Accepted Answer

To accommodate proteins with longer hydrophobic membrane-spanning domains.

Question 15

Which of the following is a key step in the process of posttranslational import of proteins into the ER lumen?

Accepted Answer

Association with Hsp70 chaperones to keep the protein unfolded.

Question 16

Which of the following is TRUE regarding the assembly of clathrin coats during vesicle formation?

Accepted Answer

Clathrin triskelions assemble into hexagons and pentagons to form a spherical vesicle.

Question 17

Which of the following best describes the fate of indigestible material in lysosomes?

Accepted Answer

It accumulates in residual bodies, which may be exocytosed or contribute to cellular aging.

Question 18

Which of the following is a characteristic feature of autophagy?

Accepted Answer

Degradation of damaged or unneeded cellular structures via lysosomes.

Question 19

Which of the following is a direct result of a mutation that prevents the masking of the RXR tag in NMDA receptor subunits?

Accepted Answer

NMDA receptor subunits are retained in the ER and cannot reach the plasma membrane.

Trafficking Through the Endomembrane System: Protein Sorting, Vesicular Transport, and Cellular Digestion

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