Question 1

Which of the following best describes the role of the nuclear lamina in the nucleus?

Accepted Answer

It supports the shape of the nuclear envelope and stabilizes nuclear pores.

Question 2

A protein destined for the mitochondrial matrix is synthesized in the cytosol. Which sequence of events correctly describes its import?

Accepted Answer

Protein is unfolded by chaperones, binds to a receptor on the outer membrane, passes through TOM/TIM, and is folded inside the matrix.

Question 3

Which of the following is required for the import of proteins into the nucleus?

Accepted Answer

A nuclear localization signal (NLS) and importin receptor

Question 4

During nuclear export, what is the role of Ran-GTP?

Accepted Answer

It binds to the exportin-cargo complex to facilitate movement through the nuclear pore.

Question 5

A mutation prevents the hydrolysis of Ran-GTP in the cytosol. What is the most likely consequence?

Accepted Answer

Exportin cannot release its cargo in the cytosol.

Question 6

Which of the following best explains why some proteins are synthesized on free ribosomes while others are synthesized on the rough ER?

Accepted Answer

Proteins destined for the cytosol, nucleus, mitochondria, or peroxisomes are synthesized on free ribosomes, while those for the endomembrane system or secretion are synthesized on the rough ER.

Question 7

A protein contains both a stroma-targeting sequence and a thylakoid-targeting sequence. Where will this protein ultimately localize in the chloroplast?

Accepted Answer

Thylakoid lumen

Question 8

Which of the following is TRUE regarding the import of proteins into peroxisomes?

Accepted Answer

Proteins are imported posttranslationally by peroxins and can be folded during import.

Question 9

Which of the following steps is unique to cotranslational import into the ER?

Accepted Answer

Recognition of an ER signal sequence by the signal recognition particle (SRP)

Question 10

A mutation in the gene encoding signal peptidase would most directly affect which process?

Accepted Answer

Cleavage of the ER targeting sequence from nascent polypeptides

Question 11

Which of the following best describes the orientation of a multi-pass transmembrane protein in the ER membrane?

Accepted Answer

It is determined by the number and location of start and stop transfer sequences.

Question 12

Which of the following is NOT exported from the nucleus through nuclear pores?

Accepted Answer

Histones

Question 13

A patient has a genetic defect in importin. Which cellular process would be most directly affected?

Accepted Answer

Import of proteins into the nucleus

Question 14

Which of the following best explains why chaperones are required for mitochondrial protein import?

Accepted Answer

They help proteins remain unfolded in the cytosol and assist in refolding inside the mitochondria.

Question 15

Which of the following is a key difference between posttranslational and cotranslational import?

Accepted Answer

Posttranslational import occurs after protein synthesis is complete, while cotranslational import occurs during protein synthesis.

Question 16

A protein is found to accumulate in the cytosol and not reach the peroxisome. Which is the most likely explanation?

Accepted Answer

The protein lacks a peroxisomal targeting signal.

Question 17

Which of the following best describes the function of BiP in the ER?

Accepted Answer

It acts as a chaperone, pulling proteins into the ER lumen during posttranslational import.

Question 18

Which of the following is a direct consequence of a nonfunctional TOM complex in mitochondria?

Accepted Answer

Proteins cannot be imported into the mitochondrial matrix.

Question 19

Which of the following best describes the fate of a water-soluble protein synthesized in the rough ER?

Accepted Answer

It is released into the ER lumen and may be secreted or sent to other organelles.

Protein Targeting and Sorting: Mechanisms of Cellular Compartmentalization

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