Question 1

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

Accepted Answer

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

Question 2

A newly synthesized protein lacks a signal sequence. Where is it most likely to be found after translation?

Accepted Answer

In the cytosol

Question 3

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 endoplasmic reticulum.

Question 4

Which of the following statements about ribosomes and protein synthesis is correct?

Accepted Answer

All ribosomes begin translation as free ribosomes in the cytoplasm.

Question 5

A protein has the following amino acid sequence at its N-terminus: Leu-Val-Gly-Ile-Leu-Phe-Trp-Ala-Thr-Glu. What is the most likely function of this sequence?

Accepted Answer

It serves as a signal sequence for protein targeting.

Question 6

If a protein's ER signal sequence is removed during synthesis, what is the most likely fate of the protein?

Accepted Answer

It will remain in the cytosol.

Question 7

Which of the following best explains why signal sequences are typically 15–60 amino acids long?

Accepted Answer

This length is sufficient to form a unique structure recognized by cellular transport machinery.

Question 8

A mutation changes the signal sequence of a protein so that it is no longer recognized by the ER. What is the most likely consequence?

Accepted Answer

The protein will not enter the ER and will remain in the cytosol.

Question 9

Which of the following scenarios best illustrates the concept of protein sorting in a real-world context?

Accepted Answer

A genetic disorder causes a misfolded enzyme to accumulate in the cytosol because its signal sequence is defective.

Question 10

During translation, what determines whether a ribosome will remain free in the cytosol or become attached to the ER?

Accepted Answer

The presence or absence of a signal sequence in the protein being synthesized.

Question 11

A scientist is studying a protein that is normally secreted from the cell. She finds a mutant version that accumulates in the cytosol. Which of the following is the most likely explanation?

Accepted Answer

The mutant protein lacks a functional ER signal sequence.

Question 12

Which of the following best describes the initial step in the synthesis of all proteins in eukaryotic cells?

Accepted Answer

Translation begins on free ribosomes in the cytoplasm.

Question 13

A protein is found in the ER lumen. Which of the following must have occurred during its synthesis?

Accepted Answer

It was synthesized with an ER signal sequence that directed the ribosome to the ER.

Question 14

Which of the following is a direct consequence of adding an ER signal sequence to a normally cytosolic protein?

Accepted Answer

The protein will be targeted to the ER during translation.

Question 15

A patient has a genetic mutation that prevents the removal of the ER signal sequence from a protein after it enters the ER. What is the most likely effect on the protein?

Accepted Answer

The protein may be misfolded or improperly processed in the ER.

Question 16

Which of the following best explains why the addition of an ER signal sequence to a cytosolic protein can be used as a tool in biotechnology?

Accepted Answer

It allows researchers to direct the protein to the ER for secretion or further modification.

Protein Sorting and Signal Sequences in Eukaryotic Cells

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