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 3

Chapter 13, Problem 3

A virus with RNA-dependent RNA polymerase
a. synthesizes DNA from an RNA template.
b. synthesizes double-stranded RNA from an RNA template.
c. synthesizes double-stranded RNA from a DNA template.
d. transcribes mRNA from DNA.
e. none of the above

Verified step by step guidance

Step 1: Understand the function of RNA-dependent RNA polymerase (RdRp). This enzyme synthesizes RNA from an RNA template, which is a key feature of certain RNA viruses.

Step 2: Analyze each option in the context of RdRp activity: (a) synthesizes DNA from RNA template - this describes reverse transcriptase, not RdRp.

Step 3: Consider option (b) synthesizes double-stranded RNA from an RNA template - this matches the activity of RdRp, which can create complementary RNA strands to form double-stranded RNA.

Step 4: Evaluate options (c) and (d): (c) synthesizes double-stranded RNA from DNA template - this is incorrect because RdRp uses RNA, not DNA, as a template; (d) transcribes mRNA from DNA - this is the role of DNA-dependent RNA polymerase, not RdRp.

Step 5: Conclude that the correct description of RNA-dependent RNA polymerase activity is option (b), synthesizing double-stranded RNA from an RNA template.

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Key Concepts

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

RNA-dependent RNA polymerase (RdRp)

RNA-dependent RNA polymerase is an enzyme used by RNA viruses to replicate their RNA genomes. It synthesizes a complementary RNA strand using an RNA template, enabling the production of new viral RNA. This enzyme is essential for RNA virus replication but is not involved in DNA synthesis.

RNA virus replication mechanisms

RNA viruses replicate their genomes by synthesizing RNA from RNA templates, often producing double-stranded RNA intermediates. This process differs from DNA viruses, which use DNA-dependent enzymes. Understanding this mechanism helps distinguish how viral RNA is copied and how mRNA is produced for protein synthesis.

Transcription and reverse transcription

Transcription typically refers to synthesizing RNA from a DNA template, while reverse transcription involves making DNA from an RNA template. RNA-dependent RNA polymerase does not perform these functions; instead, it synthesizes RNA from RNA, distinguishing it from DNA-dependent RNA polymerase and reverse transcriptase.

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Related Practice

Textbook Question

List the four properties that define a virus. What is a virion?

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Textbook Question

Describe the four morphological classes of viruses, then diagram and give an example of each.

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Textbook Question

Which of the following would be the first step in the biosynthesis of a virus with reverse transcriptase?

a. A complementary strand of RNA must be synthesized.

b. Double-stranded RNA must be synthesized.

c. A complementary strand of DNA must be synthesized from an RNA template.

d. A complementary strand of DNA must be synthesized from a DNA template.

e. None of the above

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Textbook Question

Place the following in the most likely order for biosynthesis of a bacteriophage: (1) phage lysozyme; (2) mRNA; (3) DNA; (4) viral proteins; (5) DNA polymerase.

a. 5, 4, 3, 2, 1

b. 1, 2, 3, 4, 5

c. 5, 3, 4, 2, 1

d. 3, 5, 2, 4, 1

e. 2, 5, 3, 4, 1

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Textbook Question

Label the principal events of attachment, biosynthesis, entry, and maturation of a + stranded RNA virus. Draw in uncoating.

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Textbook Question