Question 1

Which of the following targeting sequences is responsible for importing proteins into the nucleus?

Accepted Answer

Nuclear localization signal (NLS)

Question 2

A mutation in the gene encoding the signal recognition particle (SRP) would most likely result in which cellular defect?

Accepted Answer

Impaired targeting of proteins to the endoplasmic reticulum

Question 3

Which of the following best describes the role of the signal peptidase during protein translocation into the ER?

Accepted Answer

It cleaves the signal sequence from the nascent protein

Question 4

A patient’s cells accumulate misfolded glycoproteins in the ER. Which process is most likely defective?

Accepted Answer

ER-associated degradation (ERAD)

Question 5

Which vesicle coat protein is primarily responsible for retrograde transport from the Golgi to the ER?

Accepted Answer

COPI

Question 6

A protein destined for the lysosome is tagged in the cis-Golgi with which modification?

Accepted Answer

Phosphorylation of mannose residues

Question 7

Which of the following best explains why most proteins must be translocated co-translationally into the ER?

Accepted Answer

Folded proteins cannot pass through the translocation channel

Question 8

Which of the following is a function of the smooth endoplasmic reticulum (SER) in Leydig cells?

Accepted Answer

Synthesis of steroid hormones

Question 9

Which of the following best describes the function of Rab proteins in vesicular transport?

Accepted Answer

They recruit tethering proteins to ensure vesicle targeting specificity

Question 10

Which of the following steps is NOT involved in the synthesis of an integral membrane protein in the ER?

Accepted Answer

Cleavage of all start-transfer sequences by signal peptidase

Question 11

Which of the following best explains the maintenance of membrane asymmetry in eukaryotic cells?

Accepted Answer

Transverse diffusion (flip-flop) is catalyzed by flippases

Question 12

A researcher observes that a protein with a nuclear export signal (NES) accumulates in the nucleus. Which process is most likely impaired?

Accepted Answer

Export from the nucleus

Question 13

Which of the following is TRUE regarding the cisternal maturation model of Golgi transport?

Accepted Answer

Each cisterna matures as it moves from the cis to the trans face

Question 14

Which of the following best describes the fate of misfolded proteins that cannot be refolded in the ER?

Accepted Answer

They are translocated to the cytosol and degraded by the proteasome

Question 15

Which of the following is a key function of clathrin-coated vesicles?

Accepted Answer

Transport from the TGN to endosomes and lysosomes

Question 16

A protein is synthesized in the cytosol and contains a mitochondrial targeting sequence (MTS). What must happen for it to be imported into the mitochondrion?

Accepted Answer

It must remain unfolded and interact with the TOM and TIM complexes

Question 17

Which of the following best describes the process of exocytosis?

Accepted Answer

It involves fusion of a secretory vesicle with the plasma membrane

Question 18

Which of the following is the correct sequence of events for the co-translational translocation of a secretory protein into the ER?

Accepted Answer

SRP binds signal sequence → SRP-ribosome complex binds SRP receptor → Ribosome binds translocator → SRP released → Translation resumes

Question 19

Which of the following is a consequence of defective glycosyltransferase activity in the Golgi apparatus?

Accepted Answer

Glycoproteins lack proper carbohydrate modifications

Question 20

Which of the following best explains why folded proteins cannot be imported into mitochondria?

Accepted Answer

The TOM and TIM complexes only accommodate unfolded polypeptides

The Endomembrane System: Protein Targeting, ER, and Golgi Function

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