Question 1

Which of the following best describes the role of chaperone proteins, such as Hsp70, during the import of proteins into mitochondria?

Accepted Answer

They keep the protein unfolded in the cytosol to allow passage through mitochondrial membranes.

Question 2

A scientist mutates the nuclear localization signal (NLS) of a protein. What is the most likely outcome for this protein in a eukaryotic cell?

Accepted Answer

The protein will remain in the cytosol and not be imported into the nucleus.

Question 3

Which of the following statements about nuclear import is correct?

Accepted Answer

Nuclear import requires energy, often provided by GTP hydrolysis.

Question 4

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

Accepted Answer

The protein is kept unfolded by chaperones, its signal sequence binds to a receptor on the outer mitochondrial membrane, and it is translocated into the matrix.

Question 5

Which of the following is a key difference between protein import into the nucleus and into mitochondria?

Accepted Answer

Proteins imported into the nucleus are typically folded, while those imported into mitochondria are kept unfolded.

Question 6

A mutation prevents the interaction between cytosolic fibrils and nuclear import receptors. What is the most likely consequence?

Accepted Answer

Proteins with nuclear localization signals will not be efficiently imported into the nucleus.

Question 7

Which of the following best explains why energy is required for nuclear import?

Accepted Answer

Energy is needed to move large, folded proteins against a concentration gradient through the nuclear pore complex.

Question 8

A researcher is studying a protein that is normally localized to the nucleus. She attaches a mitochondrial targeting sequence to this protein. Where is the protein most likely to be found?

Accepted Answer

In the mitochondria, because the mitochondrial targeting sequence overrides the nuclear localization signal.

Question 9

Which of the following is true regarding the import of proteins into chloroplasts and mitochondria?

Accepted Answer

Both require specific signal sequences and the assistance of chaperone proteins to keep the protein unfolded during import.

Question 10

A patient has a genetic disorder that affects the function of Hsp70 chaperone proteins. Which cellular process is most likely to be directly impaired?

Accepted Answer

Import of proteins into mitochondria and chloroplasts.

Question 11

Which of the following equations best represents the energy requirement for nuclear import, where $$\Delta G is $$the change in free energy, $$G_{final} is $$the free energy after import, and $$G_{initial} is $$the free energy before import?

Accepted Answer

$$\Delta G = G_{final} - G_{initial}$$

Question 12

A protein is found to accumulate in the cytosol rather than the nucleus. Which of the following is the most likely explanation?

Accepted Answer

The protein lacks a functional nuclear localization signal.

Question 13

Which of the following best describes the function of nuclear import receptors?

Accepted Answer

They recognize and bind to nuclear localization signals on cargo proteins.

Question 14

During the import of a protein into the mitochondrial matrix, which of the following steps occurs first?

Accepted Answer

Hsp70 chaperone binds to the polypeptide to keep it unfolded.

Question 15

A mutation in the gene encoding a nuclear import receptor would most likely result in which of the following cellular phenotypes?

Accepted Answer

Accumulation of nuclear proteins in the cytosol.

Cellular Internal Structures and Protein Transport Mechanisms

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