Question 1

A researcher is using the spread-plate method to estimate the number of bacteria in a water sample. After plating 0.1 mL of a 10^-4 dilution, she counts 75 colonies. What is the estimated concentration of bacteria in the original sample (in CFU/mL)?

Accepted Answer

$$7.5 	imes 10^6$

Question 2

Which of the following best describes the function of the RecA protein in bacterial cells?

Accepted Answer

It is essential for homologous recombination and the SOS DNA repair response.

Question 3

A bacterial culture is in the log (exponential) phase of growth. If the initial cell number is $$1 	imes 10^5$ and the generation time is 30 minutes, how many cells will there be after 2 hours?

Accepted Answer

$$1.6 	imes 10^6$

Question 4

Which adaptation is most likely found in thermophilic bacteria to maintain protein stability at high temperatures?

Accepted Answer

Increased number of ionic bonds and hydrophobic interactions in proteins

Question 5

A mutation changes a codon from UAU (tyrosine) to UAA (stop codon). What type of mutation is this?

Accepted Answer

Nonsense mutation

Question 6

Which of the following statements about the lac operon in E. coli is correct?

Accepted Answer

The lac operon is maximally expressed when lactose is present and glucose is absent.

Question 7

Which enzyme is responsible for removing supercoils ahead of the replication fork during bacterial DNA replication?

Accepted Answer

DNA gyrase

Question 8

A patient is infected with a bacterium that can survive in the presence of oxygen but does not use it for growth. Which term best describes this organism?

Accepted Answer

Aerotolerant anaerobe

Question 9

Which of the following best explains why halophilic microorganisms can survive in high-salt environments?

Accepted Answer

They accumulate compatible solutes to balance osmotic pressure.

Question 10

Which of the following is a function of alternate sigma factors in bacteria?

Accepted Answer

They allow RNA polymerase to recognize different sets of promoters under stress conditions.

Question 11

A bacterium is exposed to UV light, resulting in thymine dimers. Which DNA repair mechanism is most likely to be activated first?

Accepted Answer

Excision repair

Question 12

Which of the following best describes the process of generalized transduction in bacteria?

Accepted Answer

A bacteriophage accidentally packages host DNA and transfers it to another bacterium.

Question 13

Which of the following is a key difference between the lytic and lysogenic cycles of bacteriophage lambda?

Accepted Answer

In the lysogenic cycle, the phage genome integrates into the host chromosome as a prophage.

Question 14

A scientist is studying a +RNA virus. Which of the following statements about its replication is correct?

Accepted Answer

The viral genome can serve directly as mRNA for translation.

Question 15

Which of the following best explains antigenic shift in influenza viruses?

Accepted Answer

Reassortment of genome segments from different viral strains infecting the same cell

Question 16

Which of the following is a role of chaperone proteins in bacterial cells?

Accepted Answer

They assist in the proper folding of newly synthesized proteins.

Question 17

A bacterial cell is exposed to a chemical mutagen that causes the insertion of a single nucleotide into a coding sequence. What is the most likely result?

Accepted Answer

Frameshift mutation

Question 18

Which of the following best describes the function of the CRP-cAMP complex in the regulation of the lac operon?

Accepted Answer

It acts as a transcriptional activator when glucose is low.

Question 19

Which of the following is a characteristic of the F-plasmid in E. coli?

Accepted Answer

It can integrate into the host chromosome and mediate conjugation.

Question 20

A patient is infected with a retrovirus. Which enzyme is essential for the replication of this virus?

Accepted Answer

Reverse transcriptase

Microbial Growth, Molecular Biology, Gene Regulation, Mutation, and Viral Diversity: Study Notes for Exam 2 (Biology 331)

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