Question 1

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

Accepted Answer

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

Question 2

A newly synthesized protein destined for the mitochondria is transported post-translationally. Which of the following is TRUE about this process?

Accepted Answer

The protein is kept unfolded by chaperones until it passes through mitochondrial membranes.

Question 3

Which cellular structure serves as the gateway for molecules entering or exiting the nucleus?

Accepted Answer

Nuclear pore complex

Question 4

What determines whether a ribosome remains free in the cytosol or becomes attached to the endoplasmic reticulum?

Accepted Answer

The presence of an ER signal sequence in the protein being synthesized

Question 5

Which of the following best explains why proteins destined for secretion are synthesized on ribosomes attached to the ER?

Accepted Answer

Co-translational transport allows the protein to enter the ER lumen as it is being synthesized.

Question 6

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

Accepted Answer

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

Question 7

Which process involves the transport of a fully synthesized protein to its destination after translation is complete?

Accepted Answer

Post-translational transport

Question 8

Which of the following is a function of chaperone proteins during mitochondrial protein import?

Accepted Answer

They keep the polypeptide unfolded to facilitate passage through the mitochondrial membrane.

Question 9

Which equation best represents the energy requirement for active transport of proteins through the nuclear pore complex?

Accepted Answer

$$ ATP \rightarrow ADP + P_i $$

Question 10

A protein with a nuclear localization signal (NLS) is synthesized in the cytosol. What is the correct sequence of events for its import into the nucleus?

Accepted Answer

Binding to import receptor, passage through nuclear pore, release into nucleus

Question 11

Which of the following is TRUE about the endomembrane system in eukaryotic cells?

Accepted Answer

It includes the ER, Golgi apparatus, lysosomes, and vesicles involved in protein sorting.

Question 12

During co-translational transport, which event occurs as the protein is being synthesized?

Accepted Answer

The protein is inserted into the ER membrane or lumen while translation is ongoing.

Question 13

Which of the following best describes the fate of membrane proteins synthesized on the rough ER?

Accepted Answer

They are inserted into the ER membrane and may be trafficked to other membranes via vesicles.

Question 14

A scientist 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 membranes.

Question 15

Which organelle is primarily responsible for recycling cellular material through hydrolytic enzymes?

Accepted Answer

Lysosome

Question 16

Which of the following is a multi-step process involving both protein synthesis and vesicular transport?

Accepted Answer

Secretion of insulin from pancreatic beta cells

Question 17

Which statement best explains the collaboration of internal cell structures in protein sorting?

Accepted Answer

Organelles and molecular signals work together to ensure proteins reach their correct destinations.

Question 18

Which of the following is a consequence of a defective nuclear pore complex?

Accepted Answer

Impaired transport of proteins and RNA between the nucleus and cytoplasm

Question 19

Which formula would you use to calculate the number of possible signal sequences of length $$n$$ using $$20$$ amino acids?

Accepted Answer

$$ 20^n $$

Protein Sorting and Transport Inside Eukaryotic Cells

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