Question 1

Which of the following best describes the role of quorum sensing in bacterial biofilm formation?

Accepted Answer

It allows bacteria to sense and respond to population density by regulating gene expression, leading to coordinated behaviors such as biofilm formation.

Question 2

Biofilms provide ecological advantages to bacteria. Which of the following is NOT a typical advantage conferred by biofilm formation?

Accepted Answer

Decreased ability to communicate via quorum sensing

Question 3

A hospital-acquired infection is traced to a catheter colonized by a bacterial biofilm. Which property of biofilms most likely contributed to the persistence of this infection despite antibiotic treatment?

Accepted Answer

Biofilms create a physical barrier that limits antibiotic penetration, allowing bacteria within to survive.

Question 4

Which of the following best describes the environmental stress response in bacteria?

Accepted Answer

It is a set of physiological changes that allow bacteria to survive sudden changes in their environment, such as osmotic shock or temperature shifts.

Question 5

During osmotic stress, mechanosensitive channels in bacterial membranes open. What is the primary function of these channels?

Accepted Answer

To allow solutes to exit the cell rapidly, preventing cell lysis due to sudden decreases in external osmolarity.

Question 6

Cells entering stationary phase are more resistant to oxidative stress. Which enzyme is crucial for detoxifying toxic oxygen products in bacteria?

Accepted Answer

Catalase

Question 7

Which of the following best describes the heat-shock response in E. coli after a temperature shift from $$30^\circC to$$ $$42^\circC$$?

Accepted Answer

The rate of synthesis of heat-shock proteins increases relative to other proteins, helping the cell cope with protein denaturation.

Question 8

Which of the following is NOT a role of heat-shock proteins (Hsps) in bacteria?

Accepted Answer

Synthesizing new DNA during cell division

Question 9

A mutant E. coli strain cannot grow above $$20^\circC $$due to a deficiency in a key regulatory protein for heat-shock protein synthesis. Which protein is most likely deficient?

Accepted Answer

$$\$$sigma^{32}$$ (sigma 32)

Question 10

Which of the following DNA repair mechanisms directly reverses thymine dimers caused by UV light using visible light?

Accepted Answer

Photoreactivation

Question 11

In nucleotide excision repair, which enzyme is responsible for cutting nucleotides away on either side of a DNA dimer?

Accepted Answer

Endonuclease

Question 12

The SOS response in bacteria is triggered by which of the following cellular events?

Accepted Answer

Accumulation of single-stranded DNA due to stalled replication at sites of DNA damage

Question 13

Which of the following is a common source of oxidative stress in bacteria?

Accepted Answer

Exposure to reactive oxygen species produced by host immune cells during phagocytosis

Question 14

Which of the following best explains why strict anaerobes are sensitive to oxygen?

Accepted Answer

They lack enzymes such as catalase or superoxide dismutase required to detoxify reactive oxygen species.

Question 15

A bacterial cell exposed to UV light develops thymine dimers in its DNA. Which repair mechanism would be most effective if the cell is subsequently exposed to visible light?

Accepted Answer

Photoreactivation, which uses photolyase to cleave the dimer upon absorption of visible light

Question 16

Which of the following steps is NOT part of the nucleotide excision repair pathway?

Accepted Answer

Direct cleavage of thymine dimers by photolyase

Question 17

Which of the following is a real-world example of quorum sensing influencing bacterial behavior?

Accepted Answer

Vibrio fischeri producing bioluminescence only at high cell densities in the light organ of certain squid

Question 18

Which of the following best describes the function of the SOS response in bacteria?

Accepted Answer

It induces the expression of DNA repair enzymes in response to extensive DNA damage, allowing survival but increasing mutation rates.

Question 19

Which of the following types of DNA damage is NOT typically repaired by nucleotide excision repair?

Accepted Answer

Single base mismatches

Quorum Sensing, Biofilm Formation, and Environmental Stress Responses in Microorganisms (lecture 7a)

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