Question 1

Which of the following best describes the primary function of the rough endoplasmic reticulum (RER) in eukaryotic cells?

Accepted Answer

Synthesis and initial processing of proteins destined for the endomembrane system or secretion

Question 2

A patient is prescribed a new medication but experiences severe side effects, while most patients tolerate it well. Genetic analysis reveals a variant in a cytochrome P-450 gene. Which field of study investigates such differences in drug response?

Accepted Answer

Pharmacogenetics

Question 3

Which of the following best explains why cells that produce large amounts of steroid hormones have extensive smooth endoplasmic reticulum (SER)?

Accepted Answer

SER contains enzymes required for cholesterol and steroid biosynthesis

Question 4

A liver cell is actively breaking down glycogen to release glucose into the bloodstream. Which enzyme, located in the smooth ER, is directly responsible for producing free glucose from glucose-6-phosphate?

Accepted Answer

Glucose-6-phosphatase

Question 5

Which of the following best describes the process of hydroxylation in drug detoxification by the smooth ER?

Accepted Answer

Addition of a hydroxyl group to the drug, increasing its solubility

Question 6

Which of the following statements about the Golgi apparatus is correct?

Accepted Answer

The Golgi apparatus sorts and packages proteins and lipids received from the ER for transport to various destinations

Question 7

A protein destined for the lysosome is synthesized in the rough ER. Which specific tag is added in the Golgi apparatus to ensure its delivery to the lysosome?

Accepted Answer

Mannose-6-phosphate

Question 8

Which of the following best explains the difference between anterograde and retrograde transport in the endomembrane system?

Accepted Answer

Anterograde transport moves materials from the ER toward the plasma membrane, while retrograde transport returns materials from the Golgi to the ER

Question 9

A newly synthesized protein in the ER is found to be misfolded. Which of the following best describes the fate of this protein?

Accepted Answer

It is exported to the cytosol and degraded by proteasomes

Question 10

Which of the following is a key function of the signal recognition particle (SRP) during cotranslational import?

Accepted Answer

It recognizes the ER signal sequence and directs the ribosome to the ER membrane

Question 11

A researcher creates a chimeric protein by fusing a normally secreted protein with a KDEL sequence. Where would you expect to find this protein in the cell?

Accepted Answer

In the endoplasmic reticulum

Question 12

Which of the following best explains the mechanism by which integral membrane proteins are inserted into the ER membrane?

Accepted Answer

They are cotranslationally inserted into the ER membrane, with stop-transfer and start-transfer sequences determining their orientation

Question 13

Which of the following best describes the role of flippases in membrane biosynthesis?

Accepted Answer

They transfer newly synthesized phospholipids from the cytosolic to the lumenal leaflet of the ER membrane

Question 14

A mutation causes the hydrophobic domain of a Golgi-resident protein to be longer than normal. What is the most likely consequence?

Accepted Answer

The protein will migrate to later (thicker) compartments of the Golgi or even to the plasma membrane

Question 15

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 16

Which of the following best describes the process of N-linked glycosylation?

Accepted Answer

Addition of an oligosaccharide to the nitrogen atom of asparagine residues

Question 17

A muscle cell is unable to contract due to a defect in calcium storage. Which organelle is most likely malfunctioning?

Accepted Answer

Sarcoplasmic reticulum (a specialized smooth ER)

Question 18

Which of the following best explains the role of the unfolded protein response (UPR) in the ER?

Accepted Answer

It detects misfolded proteins and activates pathways to reduce protein synthesis and increase folding capacity

Question 19

A secretory protein is labeled with a radioactive amino acid. After 3 minutes, the label is found in the rough ER; after 37 minutes, it is found in vesicles budding from the Golgi. What does this experiment demonstrate?

Accepted Answer

Proteins move sequentially from the ER to the Golgi and then to secretory vesicles before secretion

The Endomembrane System and Protein Sorting: Structure, Function, and Trafficking in Eukaryotic Cells

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