Ch. 13 - Viruses, Viroids, and Prions

Tortora - Microbiology: An Introduction 14th Edition

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Tortora 14th Edition

Ch. 13 - Viruses, Viroids, and Prions

Problem 7

Chapter 13, Problem 7

Which of the following statements is false?
a. Viruses contain DNA or RNA.
b. The nucleic acid of a virus is surrounded by a protein coat.
c. Viruses multiply inside living cells using viral mRNA, tRNA, and ribosomes.
d. Viruses cause the synthesis of specialized infectious elements.
e. Viruses multiply inside living cells.

Verified step by step guidance

Step 1: Understand the basic structure of viruses. Viruses contain either DNA or RNA as their genetic material, but not both simultaneously. This supports statement (a).

Step 2: Recognize that the nucleic acid of a virus is enclosed within a protein coat called a capsid, which protects the viral genome. This confirms statement (b).

Step 3: Analyze how viruses replicate. Viruses rely on the host cell's machinery, including ribosomes and tRNA, to translate viral mRNA into proteins. However, viruses do not have their own tRNA or ribosomes; they use the host's. This means statement (c) is partially incorrect because viruses do not contain their own tRNA and ribosomes.

Step 4: Consider the meaning of statement (d). Viruses cause the synthesis of viral components (proteins and nucleic acids) but not 'specialized infectious elements' as a separate entity. This statement is ambiguous and likely false because viruses themselves are the infectious elements.

Step 5: Confirm that viruses multiply inside living cells by hijacking the host's cellular machinery, which supports statement (e).

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Structure of Viruses

Viruses consist of genetic material, either DNA or RNA, enclosed within a protective protein coat called a capsid. This simple structure allows them to infect host cells and protect their nucleic acid from degradation.

Viral Replication Mechanism

Viruses replicate by hijacking the host cell's machinery, using the host's ribosomes and enzymes to produce viral proteins and nucleic acids. However, viruses do not possess their own tRNA or ribosomes; they rely entirely on the host's components.

Role of Viral mRNA and Infectious Elements

Viral mRNA is synthesized inside the host cell to direct the production of viral proteins. Viruses do not cause the synthesis of specialized infectious elements; rather, the virus itself is the infectious agent that assembles new viral particles within the host.

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Textbook Question

Place the following in the order in which they are found in a host cell: (1) capsid proteins;

(2) infective phage particles; (3) phage nucleic acid.

a. 1, 2, 3

b. 3, 2, 1

c. 2, 1,3

d. 3, 1, 2

e. 1, 3, 2

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Textbook Question

The ability of a virus to infect an organism is regulated by

a. the host species.

b. the type of cells.

c. the availability of an attachment site.

d. cell factors necessary for viral replication.

e. all of the above

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Textbook Question

Recall from Chapter 1 that Koch's postulates are used to determine the etiology of a

disease. Why is it difficult to determine the etiology of

a. a viral infection, such as influenza?

b. cancer?

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Textbook Question

Plant viruses can’t penetrate intact plant cells because (a) ________; therefore, they enter cells by (b) ________. Plant viruses can be cultured in (c) ________.

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Textbook Question

Persistent viral infections such as (a) ________ might be caused by (b) ________ that are (c) ________.

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Textbook Question

Some antibiotics activate phage genes. MRSA releasing Panton-Valentine leukocidin is a toxin that can cause a life-threatening disease. Why can such a disease develop following antibiotic treatment?

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