Question 1

Which of the following best explains why viruses are considered obligate intracellular parasites?

Accepted Answer

They require host cell machinery for DNA replication, transcription, and translation.

Question 2

A bacteriophage infects a bacterial cell and immediately begins replicating, ultimately causing the cell to lyse. What type of replication cycle is this?

Accepted Answer

Lytic cycle

Question 3

Which of the following is TRUE regarding the structure of a typical virus?

Accepted Answer

The viral genome can be either DNA or RNA, and may be single or double stranded.

Question 4

Which equation correctly represents the process of reverse transcription in retroviruses?

Accepted Answer

$$RNA \rightarrow DNA \rightarrow mRNA \rightarrow protein$$

Question 5

A scientist discovers a virus with a single-stranded RNA genome that serves directly as mRNA upon infection. According to the Baltimore classification, which class does this virus belong to?

Accepted Answer

Class IV: Positive-sense single-stranded RNA viruses

Question 6

Which of the following best describes the role of the CRISPR-Cas system in bacteria?

Accepted Answer

It provides bacteria with a memory of previous viral infections, enabling targeted destruction of viral DNA.

Question 7

During the replication of enveloped viruses such as HIV, which step involves the fusion of the viral envelope with the host cell membrane?

Accepted Answer

Membrane fusion

Question 8

Which of the following statements about bacteriophages is CORRECT?

Accepted Answer

Bacteriophages are viruses that infect bacteria and can undergo both lytic and lysogenic cycles.

Question 9

A virus with a negative-sense single-stranded RNA genome must first synthesize which molecule before it can produce viral proteins?

Accepted Answer

Positive-sense RNA (mRNA)

Question 10

Which of the following best describes the function of GP120 glycoprotein in HIV infection?

Accepted Answer

It binds to the CD4 receptor on immune cells, facilitating viral entry.

Question 11

Which of the following mechanisms allows bacteria to defend against viral infection by phages?

Accepted Answer

Restriction enzymes that cut foreign DNA

Question 12

A virus is found to have a circular double-stranded DNA genome and infects bacteria. Which type of virus is this most likely to be?

Accepted Answer

Bacteriophage

Question 13

Which step in the CRISPR-Cas system involves the destruction of invading viral DNA?

Accepted Answer

Step 3: Cas protein uses crRNA to find and cut matching viral DNA sequences

Question 14

Which of the following best describes the difference between non-enveloped and enveloped viruses during host cell entry?

Accepted Answer

Non-enveloped viruses enter by endocytosis, while enveloped viruses enter by membrane fusion.

Question 15

Which of the following is a correct sequence for the general steps of viral replication in a host cell?

Accepted Answer

1. Disassembly of viral particle; 2. Replication of viral genome; 3. Synthesis of viral proteins; 4. Release

Question 16

A virus infects a cell and integrates its genome into the host's chromosome, remaining dormant until activated. What is this form of the virus called?

Accepted Answer

Provirus

Question 17

Which of the following is a plausible consequence if a bacterium loses its restriction enzyme genes?

Accepted Answer

It will be more susceptible to infection by bacteriophages.

Question 18

Which of the following best describes the role of the viral capsid?

Accepted Answer

It encloses and protects the viral genome.

Question 19

A patient is infected with a virus that uses host cell ribosomes to translate its mRNA into proteins. Which type of viral genome does this virus most likely possess?

Accepted Answer

Positive-sense single-stranded RNA

Question 20

Which of the following is a real-world example of a virus that uses reverse transcriptase to replicate its genome?

Accepted Answer

HIV (Human Immunodeficiency Virus)

Viruses: Structure, Replication, and Host Interactions

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