Question 1

Which of the following best describes the role of Rab proteins in vesicle targeting and fusion?

Accepted Answer

Rab proteins (monomeric GTPases) guide vesicles to their target membranes by interacting with Rab effectors, facilitating tethering before SNARE-mediated docking and fusion.

Question 2

During the formation of COPII-coated vesicles at the ER, which of the following is TRUE regarding cargo selection?

Accepted Answer

Cargo receptors recognize exit signals on both membrane and soluble cargo proteins, ensuring their inclusion in COPII vesicles.

Question 3

Which amino acid sequence is recognized by the KDEL receptor for retrieval of ER-resident proteins from the Golgi apparatus?

Accepted Answer

Lys-Asp-Glu-Leu

Question 4

What is the main function of SNARE proteins in vesicular transport?

Accepted Answer

They mediate the fusion of lipid bilayers between vesicles and target membranes.

Question 5

A mutation in the gene encoding oligosaccharyl transferase would most directly affect which process?

Accepted Answer

N-linked glycosylation of proteins at asparagine residues in the ER lumen

Question 6

Which of the following best explains why most signal molecules bind to cell-surface receptors rather than intracellular receptors?

Accepted Answer

Most signal molecules are hydrophilic and cannot cross the plasma membrane.

Question 7

Which of the following modifications occurs primarily in the cis Golgi cisternae?

Accepted Answer

Removal of mannose

Question 8

A patient has a genetic defect that prevents the formation of mannose-6-phosphate (M6P) on lysosomal hydrolases. Which cellular process will be most directly affected?

Accepted Answer

Transport of lysosomal enzymes from the Golgi to endosomes

Question 9

Which of the following best describes the difference between the constitutive and regulated secretory pathways?

Accepted Answer

The regulated pathway requires a specific stimulus for vesicle fusion with the plasma membrane, while the constitutive pathway operates continuously.

Question 10

Which of the following is a function of protein glycosylation in the ER?

Accepted Answer

It prevents improperly folded proteins from exiting the ER.

Question 11

Which of the following best describes the role of COPI-coated vesicles?

Accepted Answer

They mediate the retrograde transport of proteins from the Golgi and vesicular tubular clusters back to the ER.

Question 12

A researcher observes that a certain protein is only glycosylated when the sequence Asn-X-Ser or Asn-X-Thr is present. What is the most likely explanation for this observation?

Accepted Answer

N-linked glycosylation specifically targets asparagine residues in these consensus sequences.

Question 13

Which of the following is a key feature of receptor-mediated endocytosis?

Accepted Answer

It uses clathrin-coated vesicles to selectively concentrate and internalize specific macromolecules bound to cell surface receptors.

Question 14

Which of the following second messengers is responsible for opening Ca$$^{2+}$$ channels in the endoplasmic reticulum?

Accepted Answer

Inositol 1,4,5-triphosphate (IP$$_3)$$

Question 15

A cell is unable to efficiently retrieve its ER-resident proteins from the Golgi. Which of the following is the most likely cause?

Accepted Answer

A mutation in the gene encoding the KDEL receptor

Question 16

Which of the following best describes the directionality of vesicular transport between the ER and Golgi apparatus?

Accepted Answer

COPII-coated vesicles mediate anterograde transport from the ER to the Golgi, while COPI-coated vesicles mediate retrograde transport from the Golgi to the ER.

Question 17

Which of the following is a real-life example of regulated exocytosis?

Accepted Answer

Release of insulin from pancreatic β cells in response to increased blood glucose

Question 18

Which of the following best explains why phagocytosis is important for animal physiology?

Accepted Answer

It allows cells to ingest large particles, such as invading microorganisms and dead cells, playing a key role in defense and tissue homeostasis.

Question 19

Which of the following best describes the fate of proteins entering the cis Golgi network?

Accepted Answer

They may be further modified, sorted, or sent back to the ER depending on their signals.

19: Intracellular Transport and Protein Sorting in Eukaryotic Cells

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