Question 1

Which of the following best describes the primary function of molecular chaperones in protein processing?

Accepted Answer

They assist in the folding and refolding of proteins, preventing misfolding and aggregation.

Question 2

A newly synthesized protein in E. coli contains a signal sequence at its N-terminus. What is the most likely role of this sequence?

Accepted Answer

It signals a secretory system to translocate the protein across a membrane.

Question 3

Which of the following statements about the Sec and Tat protein secretion systems is correct?

Accepted Answer

The Tat system exports proteins that must be folded before transport, often because they contain cofactors.

Question 4

In the context of heat shock response, which of the following best explains the role of chaperones?

Accepted Answer

They attempt to refold partially denatured proteins, preserving cellular function during stress.

Question 5

A protein in E. coli fails to fold correctly after initial chaperone assistance by DnaK and DnaJ. What is the next step in its folding pathway?

Accepted Answer

It is transferred to the GroEL-GroES complex for further folding.

Question 6

Which of the following is a key difference between the Sec and Tat protein translocase systems?

Accepted Answer

The Sec system exports unfolded proteins, while the Tat system exports folded proteins.

Question 7

A researcher mutates the signal sequence of a secreted protein, removing the positively charged residues. What is the most likely consequence?

Accepted Answer

The protein will not be recognized by the secretory system and will remain in the cytoplasm.

Question 8

Which of the following best describes the role of the GroEL-GroES complex in E. coli?

Accepted Answer

It provides an isolated environment for ATP-dependent protein folding.

Question 9

Which secretion systems in gram-negative bacteria require two steps to move proteins outside the cell?

Accepted Answer

Types II and V

Question 10

A protein destined for the periplasm of a gram-negative bacterium is found to be fully folded in the cytoplasm and contains a twin arginine signal sequence. Which secretion system will most likely transport this protein?

Accepted Answer

Tat system

Question 11

Which of the following is a function of RNA chaperones in the cell?

Accepted Answer

They assist in untangling and proper folding of RNA molecules.

Question 12

During a sudden drop in temperature, which cellular response is most likely to be upregulated in bacteria?

Accepted Answer

Cold shock protein and RNA chaperone synthesis

Question 13

Which of the following best explains why some proteins must be exported in an unfolded state via the Sec system?

Accepted Answer

Folding could interfere with their passage through the translocase channel.

Question 14

A gram-negative bacterium uses a secretion system that functions like a syringe to inject toxins directly into a host cell. Which type of secretion system is this most likely to be?

Accepted Answer

Type III

Question 15

Which of the following is a common feature of all protein translocase systems (Sec, Tat, and types I-VI) in bacteria?

Accepted Answer

They all involve recognition of a specific signal sequence on the substrate protein.

Question 16

Which of the following best describes the role of the signal recognition particle (SRP) in the Sec system?

Accepted Answer

It binds proteins that will be inserted into the cytoplasmic membrane.

Question 17

A mutation in the TatBC proteins would most directly affect which cellular process?

Accepted Answer

Transport of folded, cofactor-containing proteins across the cytoplasmic membrane

Question 18

Which of the following is a plausible reason why chaperones are highly conserved across all domains of life?

Accepted Answer

Proper protein folding is essential for cellular function and survival in all organisms.

Question 19

A protein is found to require both a signal sequence and the assistance of chaperones for proper localization. Which of the following best explains this requirement?

Accepted Answer

The protein needs to be kept unfolded for secretion and properly folded after reaching its destination.

Protein Processing, Folding, and Secretion in Bacteria L17 EXAM 2

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