Question 1

Which of the following best describes a virus particle (virion)?

Accepted Answer

The extracellular form of a virus that facilitates transmission from one host cell to another.

Question 2

Which of the following statements about viral genomes is CORRECT?

Accepted Answer

Viral genomes can be either DNA or RNA, single- or double-stranded, and may be linear or circular.

Question 3

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 4

A researcher is studying a virus that has a phospholipid bilayer surrounding its nucleocapsid. Which of the following is most likely TRUE about this virus?

Accepted Answer

It is an enveloped virus and likely infects animal cells.

Question 5

Which of the following best explains why relatively few plant or bacterial viruses are enveloped?

Accepted Answer

The presence of cell walls in plants and bacteria prevents acquisition of an envelope.

Question 6

During the replication cycle of bacteriophage T4, what is the primary role of the tail fibers?

Accepted Answer

To interact with polysaccharides on the E. coli LPS layer for attachment.

Question 7

Which of the following mechanisms do prokaryotes use to protect themselves from viral infection?

Accepted Answer

Restriction endonucleases that cleave foreign DNA at specific sites.

Question 8

A scientist observes that the number of plaque-forming units is always lower than the number of viral particles counted by electron microscopy. What is the most likely explanation?

Accepted Answer

Not all virions are infectious or conditions may be inappropriate for infectivity.

Question 9

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

Accepted Answer

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

Question 10

Which of the following best describes the burst size in a one-step growth curve of virus replication?

Accepted Answer

The number of virions released per infected cell.

Question 11

A bacteriophage genome is described as 'circularly permuted' and 'terminally redundant.' What does this mean?

Accepted Answer

The same genes are present in different orders, and some DNA sequences are duplicated at both ends.

Question 12

Which of the following is TRUE regarding the function of the CI repressor protein in lambda phage lysogeny?

Accepted Answer

It prevents transcription from the lytic promoters by binding to operator regions.

Question 13

Which event triggers the induction of the lytic cycle in a lysogenic bacterium infected with lambda phage?

Accepted Answer

DNA damage in the host cell, leading to RecA-mediated cleavage of CI repressor.

Question 14

Which of the following best describes the role of reverse transcriptase in retroviruses?

Accepted Answer

It copies information from RNA to DNA, allowing integration into the host genome.

Question 15

A virus is found to cause persistent infection in animal cells. Which of the following is most likely TRUE about this infection?

Accepted Answer

Virions are released from the host cell by budding without cell lysis.

Question 16

Which of the following is a function of the gene product of the 'int' gene in lambda phage?

Accepted Answer

It integrates the phage DNA into the bacterial chromosome at specific attachment sites.

Question 17

Which of the following best explains why the efficiency of infection in a plaque assay is usually much less than 100 percent?

Accepted Answer

Some virions are inactive or conditions are inappropriate for infectivity.

Question 18

Which of the following is a distinguishing feature of rolling circle replication in phage genome replication?

Accepted Answer

It generates concatemers, which are long DNA molecules containing multiple genome copies linked end to end.

Question 19

Which of the following is TRUE about satellite phages such as P4?

Accepted Answer

They depend on a helper phage (e.g., P2) for lytic development and use its structural proteins.

Question 20

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

Accepted Answer

It inhibits the synthesis of CI repressor and promotes the lytic cycle.

Viruses and Phages: Structure, Replication, and Life Cycles

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