Question 1

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

Accepted Answer

Protein biosynthesis and initial folding of membrane-bound and secretory proteins

Question 2

A newly synthesized polypeptide destined for secretion is being translated. Which sequence of events correctly describes its entry into the endomembrane system?

Accepted Answer

The ribosome binds to the ER via a signal recognition particle, and the polypeptide is translocated into the ER lumen cotranslationally

Question 3

Which enzyme is directly responsible for releasing free glucose from glucose-6-phosphate in the smooth endoplasmic reticulum of liver cells?

Accepted Answer

Glucose-6-phosphatase

Question 4

A mutation in the gene encoding BiP (a member of the Hsp70 family) would most likely result in which of the following cellular defects?

Accepted Answer

Accumulation of improperly folded proteins in the ER lumen

Question 5

Which of the following best explains why the smooth endoplasmic reticulum (SER) is abundant in liver cells?

Accepted Answer

Liver cells are heavily involved in detoxification and carbohydrate metabolism

Question 6

During glycosylation in the ER, which molecule acts as the lipid carrier for the core oligosaccharide before it is transferred to the nascent protein?

Accepted Answer

Dolichol phosphate

Question 7

Which of the following is a function of glycosylation of proteins in the ER and Golgi apparatus?

Accepted Answer

Maintains protein stability and serves as a transport signal for vesicle packaging

Question 8

A researcher observes that a certain protein is glycosylated on the nitrogen atom of an asparagine residue. This type of glycosylation is best described as:

Accepted Answer

N-linked glycosylation

Question 9

Which of the following best describes the direction of anterograde transport in the Golgi apparatus?

Accepted Answer

From the cis-Golgi network to the trans-Golgi network

Question 10

A cell is unable to remove improperly folded proteins from the ER. Which process is most likely defective?

Accepted Answer

ER-Associated Degradation (ERAD)

Question 11

Which of the following statements about the structure and function of the rough and smooth ER is correct?

Accepted Answer

The rough ER has ribosomes attached to its cytosolic surface, while the smooth ER does not

Question 12

Which of the following best explains the necessity of both anterograde and retrograde transport in the Golgi apparatus?

Accepted Answer

To recycle Golgi enzymes and maintain proper compartmentalization

Question 13

A patient has a genetic defect that prevents the function of cytochrome P-450 enzymes. Which cellular process would be most directly affected?

Accepted Answer

Detoxification of drugs in the smooth ER

Question 14

Which of the following best describes the role of flippases in the endoplasmic reticulum?

Accepted Answer

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

Question 15

During muscle contraction, which role does the sarcoplasmic reticulum (a specialized smooth ER) play?

Accepted Answer

It stores and releases calcium ions in response to action potentials

Question 16

A protein is found to be improperly folded and is targeted for degradation. Which cellular structure is responsible for degrading this protein after it is retrotranslocated from the ER?

Accepted Answer

Proteasome

Question 17

Which of the following is a direct consequence of a defect in the translocon complex of the rough ER?

Accepted Answer

Failure to import proteins into the ER lumen during cotranslational import

Question 18

Which of the following best describes the difference in glycosylation processing between the ER and the Golgi apparatus?

Accepted Answer

The ER adds the core oligosaccharide, while the Golgi modifies and adds terminal sugars

Question 19

A scientist is studying a protein that is synthesized in the cytosol and then imported into the ER after translation is complete. Which chaperone protein is most likely involved in this process?

Accepted Answer

BiP (Binding immunoglobulin Protein)

The Endomembrane System: Structure, Function, and Protein Processing

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