Question 1

Which of the following best describes the function of a signal sequence in protein sorting within a eukaryotic cell?

Accepted Answer

It acts as a 'zip code' that directs the protein to its correct cellular destination.

Question 2

A protein destined for the nucleus contains which of the following signal sequences?

Accepted Answer

Nuclear localization sequence (NLS)

Question 3

What is the main difference between co-translational and post-translational protein transport?

Accepted Answer

Co-translational transport occurs while the protein is being synthesized, whereas post-translational transport occurs after synthesis is complete.

Question 4

A mutation removes the ER signal sequence from a protein that is normally secreted. What is the most likely consequence?

Accepted Answer

The protein will remain in the cytosol and not be secreted.

Question 5

Which of the following processes requires the protein to remain unfolded until it reaches its final destination?

Accepted Answer

Post-translational import into mitochondria and chloroplasts

Question 6

During nuclear import, what is the role of the nuclear import receptor?

Accepted Answer

It recognizes the nuclear localization signal and facilitates transport through the nuclear pore complex.

Question 7

Which of the following best describes the pathway of a secreted protein from synthesis to secretion?

Accepted Answer

Ribosome → Rough ER → Golgi apparatus → Plasma membrane

Question 8

Which energy source is required for the translocation of proteins into mitochondria?

Accepted Answer

$$\mathrm{ATP}$$

Question 9

What is the function of chaperone proteins during post-translational import into mitochondria?

Accepted Answer

They keep the protein unfolded so it can be threaded through the mitochondrial membrane.

Question 10

Which of the following modifications occurs to proteins in the rough ER before they are sent to the Golgi apparatus?

Accepted Answer

Addition of oligosaccharides (glycosylation)

Question 11

A researcher adds an ER signal sequence to a cytosolic protein. What is the most likely outcome?

Accepted Answer

The protein will be directed to the ER and may be secreted or inserted into the membrane.

Question 12

Which of the following is NOT a function of the Golgi apparatus in protein sorting?

Accepted Answer

Synthesizing proteins from mRNA templates

Question 13

Which pathway is used for the import of most mitochondrial and chloroplast proteins?

Accepted Answer

Post-translational import

Question 14

Which of the following best explains why proteins destined for the lysosome are glycosylated in the ER?

Accepted Answer

Glycosylation acts as a tag for proper sorting and delivery to the lysosome.

Question 15

A protein is synthesized on a free ribosome and contains a peroxisomal targeting signal. Where will this protein be found after translation?

Accepted Answer

In the peroxisome

Question 16

Which of the following is a key step in the regulated secretory pathway?

Accepted Answer

Vesicles fuse with the plasma membrane in response to a specific signal.

Question 17

Which process is responsible for recycling cellular material in the lysosome?

Accepted Answer

Autophagy

Question 18

A protein is found to be mislocalized in the cytosol instead of the nucleus. Which of the following is the most likely explanation?

Accepted Answer

The protein lacks a functional nuclear localization signal.

Question 19

Which of the following equations best represents the hydrolysis of ATP required for protein import into mitochondria?

Accepted Answer

$$\mathrm{ATP} + \mathrm{H_2O} ightarrow \mathrm{ADP} + \mathrm{P_i} + 	ext{energy}$$

Question 20

Which of the following is true regarding the directionality of vesicular transport in the endomembrane system?

Accepted Answer

Vesicles can transport materials both outward (exocytosis) and inward (endocytosis).

Protein Sorting and Transport Inside the Cell

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