Question 1

Which of the following best describes the difference between a naked virus and an enveloped virus?

Accepted Answer

A naked virus has only a protein capsid surrounding its genome, while an enveloped virus has an additional outer layer derived from the host cell membrane.

Question 2

Which enzyme is responsible for making a hole in the bacterial cell wall to allow viral nucleic acid entry during bacteriophage infection?

Accepted Answer

Lysozyme

Question 3

A virus with a single-stranded RNA genome that is complementary to mRNA is described as:

Accepted Answer

Minus sense

Question 4

Which of the following statements about the viral replication cycle in a permissive host is correct?

Accepted Answer

Attachment of the virion to the host cell is the initial step, followed by penetration, synthesis, assembly, and release.

Question 5

Why are there relatively few enveloped plant or bacterial viruses compared to animal viruses?

Accepted Answer

Plant and bacterial cells have cell walls that prevent the acquisition of an envelope during viral exit.

Question 6

Which of the following best explains the concept of 'burst size' in viral replication?

Accepted Answer

The number of virions released from a single infected host cell upon lysis.

Question 7

A researcher is using a plaque assay to quantify a viral stock. She observes 50 plaques on a plate after plating 0.1 mL of a 10^-6 dilution. What is the titer of the original viral stock in plaque-forming units per mL (PFU/mL)?

$$	ext{Titer} = \frac{	ext{Number of plaques}}{	ext{Volume plated (mL)}} 	imes 	ext{Dilution factor}$$

Accepted Answer

$$5 	imes 10^7$ PFU/mL

Question 8

Which of the following is a function of the T4 phage early proteins?

Accepted Answer

Enzymes needed for DNA replication and transcription

Question 9

What is the main reason why restriction endonucleases in bacteria are generally ineffective against RNA viruses?

Accepted Answer

Restriction endonucleases are specific for double-stranded DNA and do not target RNA.

Question 10

During the infection of E. coli by bacteriophage T4, which of the following events occurs immediately after the tail fibers retract and tail pins contact the cell wall?

Accepted Answer

T4 lysozyme forms a small pore in the peptidoglycan.

Question 11

Which of the following best describes the role of the CI repressor protein in lambda phage lysogeny?

Accepted Answer

It prevents transcription from the P_R and P_L promoters, maintaining the lysogenic state.

Question 12

A retrovirus contains which of the following enzymes to facilitate its replication cycle?

Accepted Answer

RNA-dependent DNA polymerase (reverse transcriptase)

Question 13

Which of the following is a key difference between the replication of prokaryotic and eukaryotic viruses?

Accepted Answer

In eukaryotes, the entire virion enters the cell, while in prokaryotes only the nucleic acid enters.

Question 14

Which of the following best explains why the timing of lysis is important in the phage life cycle?

Accepted Answer

Proper timing allows for maximal assembly of mature virions before host cell destruction.

Question 15

Which of the following is a correct statement about rolling circle replication in phage M13?

Accepted Answer

The minus strand serves as a template for the synthesis of more plus strands, which are then packaged into phage heads.

Question 16

A temperate phage can integrate its genome into the host chromosome. What is the integrated phage DNA called?

Accepted Answer

Prophage

Question 17

Which of the following is a plausible outcome of lysogenic conversion?

Accepted Answer

The host cell becomes immune to superinfection by the same phage.

Question 18

Which of the following best describes the function of the Cro protein in lambda phage?

Accepted Answer

It prevents the synthesis and binding of CI repressor, promoting the lytic cycle.

Question 19

Which of the following is a characteristic of a persistent animal virus infection?

Accepted Answer

Virions are released slowly by budding, and the host cell remains alive.

Viruses and Phages: Structure, Replication, and Life Cycles

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