Question 1

Which of the following best describes the function of a signal sequence in a newly synthesized protein?

Accepted Answer

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

Question 2

A protein destined for the mitochondria is synthesized in the cytosol. Which of the following is TRUE about its transport?

Accepted Answer

It is transported post-translationally and kept unfolded by chaperones during import.

Question 3

Which of the following best explains why all protein synthesis begins on free ribosomes in the cytosol?

Accepted Answer

The initial steps of translation are universal, and only later does the presence of a signal sequence determine the protein's final destination.

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 instead of being secreted.

Question 5

Which process is responsible for the insertion of membrane proteins into the endoplasmic reticulum (ER) membrane?

Accepted Answer

Cotranslational transport, where the protein is inserted into the ER membrane as it is being synthesized.

Question 6

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

Accepted Answer

The protein will be directed into the ER during translation.

Question 7

Which of the following best describes the role of chaperone proteins such as Hsp70 in mitochondrial protein import?

Accepted Answer

They bind to the polypeptide to keep it unfolded for translocation into the mitochondria.

Question 8

Which of the following is NOT a component of the endomembrane system?

Accepted Answer

Mitochondria

Question 9

A protein contains a nuclear localization signal (NLS). Which pathway will it most likely follow?

Accepted Answer

It will be imported into the nucleus through the nuclear pore complex.

Question 10

Which of the following best describes the 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 11

A patient has a genetic defect that prevents the removal of signal sequences from proteins after they reach their destination. Which of the following is a likely cellular consequence?

Accepted Answer

Proteins may be mislocalized or fail to function properly due to retained signal sequences.

Question 12

Which of the following best explains why proteins destined for secretion are synthesized with an ER signal sequence?

Accepted Answer

The ER signal sequence directs the ribosome to the ER membrane, allowing the protein to enter the secretory pathway.

Question 13

Which of the following is a correct sequence of events for a protein destined for the lysosome?

Accepted Answer

Synthesis on ER-bound ribosomes $$\rightarrow$$ modification in Golgi apparatus $$\rightarrow$$ packaging into vesicles $$\rightarrow$$ delivery to lysosome

Question 14

Which of the following best describes the fate of a membrane protein with both an ER signal sequence and a stop-transfer sequence?

Accepted Answer

It will be inserted into the ER membrane with a specific orientation determined by the stop-transfer sequence.

Question 15

A scientist observes that a certain protein is only found in the nucleus. Which of the following features is most likely present in this protein?

Accepted Answer

A nuclear localization signal (NLS)

Question 16

Which of the following is a real-world example of a disease caused by protein mislocalization due to a faulty signal sequence?

Accepted Answer

Cystic fibrosis, where a mutation in the CFTR gene leads to improper trafficking of the CFTR protein.

Question 17

Which of the following best describes the function of the nuclear pore complex?

Accepted Answer

It regulates the selective transport of molecules between the nucleus and cytoplasm.

Question 18

A protein is synthesized with both a mitochondrial targeting sequence and an ER signal sequence. Where is it most likely to be localized?

Accepted Answer

It will be directed to the ER, as the ER signal sequence is recognized first during translation.

Question 19

Which of the following best explains why proteins must remain unfolded during import into mitochondria and chloroplasts?

Accepted Answer

Unfolded proteins can be threaded through narrow translocation channels in the organelle membranes.

Inside the Cell – Protein Sorting and the Endomembrane System

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