Question 1

Which of the following best explains why viruses are generally not considered living organisms?

Accepted Answer

They lack independent metabolism and cannot synthesize proteins without a host.

Question 2

A scientist discovers a new infectious agent that consists of a small, circular, single-stranded RNA molecule with no protein coat and does not encode any proteins. Which type of agent is this most likely to be?

Accepted Answer

A viroid

Question 3

Which of the following statements about the host range of viruses is correct?

Accepted Answer

Host range depends on both the presence of compatible receptors and suitable internal cell factors.

Question 4

During the lytic cycle of a bacteriophage, which of the following sequences correctly describes the order of events?

Accepted Answer

Attachment → Penetration → Biosynthesis → Assembly → Release

Question 5

A patient is diagnosed with a viral infection that persists in the body with little or no production of infectious particles between reactivations. Which term best describes this type of infection?

Accepted Answer

Latent infection

Question 6

Which of the following best explains why enveloped viruses are generally more sensitive to detergents than nonenveloped viruses?

Accepted Answer

Detergents dissolve the lipid envelope, which is required for entry into host cells.

Question 7

A researcher performs a plaque assay by plating 0.2 mL of a $$10^{-5}$$ dilution of a virus sample and counts 80 plaques. What is the titer of the virus in PFU/mL?

Accepted Answer

$$4 	imes 10^7$ PFU/mL

Question 8

Which of the following is a key difference between a prophage and a provirus?

Accepted Answer

A prophage refers to integrated phage DNA in bacteria, while a provirus refers to integrated viral DNA in animal cells.

Question 9

Which of the following best describes the mechanism by which prions propagate in the host?

Accepted Answer

They induce misfolding of normal host prion proteins, amplifying the abnormal form.

Question 10

Which of the following is a real-world example of lysogenic conversion affecting human health?

Accepted Answer

A bacterium produces diphtheria toxin only after infection by a specific temperate phage.

Question 11

Which of the following best explains why living cells are required for the cultivation of viruses?

Accepted Answer

Viruses require living cells to provide the machinery for protein synthesis and genome replication.

Question 12

Which of the following is a correct sequence of events for retroviral replication?

Accepted Answer

Attachment/entry → RNA-to-DNA synthesis → Integration → RNA/protein production → Assembly/release

Question 13

A virus is found to be highly resistant to drying, acid, and detergents, and is often transmitted via the fecal-oral route. Which structural feature is most likely responsible for this resistance?

Accepted Answer

Absence of a lipid envelope (naked virus)

Question 14

Which of the following best describes the outcome of the tobacco mosaic filtration experiment?

Accepted Answer

It showed that the infectious agent could pass through a filter that retains bacteria, indicating it was not an ordinary bacterium.

Question 15

Which of the following is a mechanism by which viruses can promote the development of cancer in humans?

Accepted Answer

By inserting genetic material near proto-oncogenes or expressing proteins that disrupt cell-cycle controls

Question 16

A patient with a history of egg allergy is recommended to receive an influenza vaccine. According to current U.S. guidelines, which of the following is true?

Accepted Answer

Egg allergy requires only routine vaccination precautions for influenza vaccines, including egg-based products.

Question 17

Which of the following best describes the structure of a prion?

Accepted Answer

A misfolded protein with no nucleic acid genome

Question 18

Which of the following viruses is most directly associated with the development of cervical cancer due to its ability to interfere with tumor suppressor proteins?

Accepted Answer

Human papillomavirus (HPV)

Question 19

A cattle farmer is concerned about bovine spongiform encephalopathy (BSE) and its potential impact on human health. Which human disease is most closely linked to exposure to the BSE agent?

Accepted Answer

Variant Creutzfeldt-Jakob disease (vCJD)

Question 20

Approximately what percentage of human cancers worldwide are estimated to be associated with viral infections, according to introductory microbiology discussions?

Accepted Answer

About 15%

Viruses: Structure, Replication, and Acellular Infectious Agents – Study Notes (Microbiology Chapter 13)

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