Question 1

Which of the following best describes the lytic cycle of a bacteriophage?

Accepted Answer

The phage uses host machinery to replicate, assembles new phages, and lyses the host cell to release progeny.

Question 2

Which enzyme is responsible for cleaving foreign phage DNA in bacteria as part of the restriction-modification system?

Accepted Answer

Restriction endonuclease

Question 3

A batch culture experiment shows a burst size of 500 phages per infected cell. If you start with $$200$$ infected cells per mL, what is the expected number of phages per mL after one lytic cycle?

Accepted Answer

$$10^5$$

Question 4

Which of the following is NOT a bacterial strategy to prevent phage attachment?

Accepted Answer

Synthesis of viral capsid proteins

Question 5

In the CRISPR-Cas system, what is the primary function of the 'spacer' sequences?

Accepted Answer

They store fragments of phage DNA for future recognition.

Question 6

Which step in the bacteriophage lytic cycle directly follows genome entry?

Accepted Answer

Replication (including enzyme and nucleic acid synthesis)

Question 7

A bacterium survives a phage attack and incorporates a new spacer into its CRISPR locus. What is the next step in the CRISPR immune response?

Accepted Answer

crRNA processing

Question 8

Which of the following best explains why filamentous phages do not kill their host cells?

Accepted Answer

They extrude progeny phages through the cell envelope, allowing the host to survive but grow slowly.

Question 9

What is the role of methylase in the bacterial restriction-modification system?

Accepted Answer

It adds methyl groups to host DNA, protecting it from cleavage by restriction endonucleases.

Question 10

Which of the following is a correct sequence of events in the CRISPR-Cas immune response?

Accepted Answer

Spacer acquisition → crRNA processing → Effector stage

Question 11

A mutant bacterium lacks functional Cas proteins. Which stage of the CRISPR immune response would be directly affected?

Accepted Answer

All of the above

Question 12

Which of the following best describes the lysogenic cycle of a bacteriophage?

Accepted Answer

The phage DNA integrates into the host genome and replicates with the host without killing it.

Question 13

Which of the following is a real-world application of the CRISPR-Cas system?

Accepted Answer

Genome editing in eukaryotic cells

Question 14

If a bacteriophage infects a bacterial cell and the cell survives by cleaving the phage DNA, which bacterial defense system was most likely involved?

Accepted Answer

Restriction-modification system

Question 15

Which of the following is a plausible consequence of phage predation on the gut bacteriophage community?

Accepted Answer

Increased host population diversity

Question 16

A phage-resistant bacterial mutant is found to lack a specific outer membrane protein. What is the most likely explanation for its resistance?

Accepted Answer

The phage cannot attach to the bacterial surface.

Question 17

Which of the following equations correctly represents the calculation of burst size in a phage infection experiment?

Accepted Answer

$$	ext{Burst size} = \frac{	ext{Total number of phages released}}{	ext{Number of infected cells}}$$

Question 18

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

Accepted Answer

Only the lysogenic cycle involves integration of phage DNA into the host genome.

Question 19

Which of the following best describes the function of Cas proteins in the CRISPR system?

Accepted Answer

They cleave foreign DNA sequences matching stored spacers.

Question 20

A researcher observes that a bacterial strain is resistant to a specific phage but susceptible to others. Which mechanism is most likely responsible for this specificity?

Accepted Answer

CRISPR-Cas system targeting the specific phage DNA

Bacteriophages and Bacterial Defense Mechanisms: Genetics and Molecular Biology

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