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Ch. 19 - Viruses
Campbell - Campbell Biology 11th Edition
Urry11th EditionCampbell BiologyISBN: 9789357423311Not the one you use?Change textbook
All textbooksUrry 11th EditionCh. 19 - VirusesProblem 5
Chapter 19, Problem 5

RNA viruses require their own supply of certain enzymes because
a. Host cells rapidly destroy the viruses.
b. Host cells lack enzymes that can replicate the viral genome.
c. These enzymes translate viral mRNA into proteins.
d. These enzymes penetrate host cell membranes.

Verified step by step guidance
1
Understand that RNA viruses are a type of virus that have RNA as their genetic material, instead of DNA.
Recognize that for RNA viruses to replicate, they need to make copies of their RNA genome.
Consider the fact that host cells typically have enzymes that replicate DNA, not RNA. This is because most organisms use DNA as their genetic material.
Realize that RNA viruses must bring their own enzymes, such as RNA-dependent RNA polymerase, to replicate their RNA genome because host cells do not have these enzymes.
Conclude that the correct reason RNA viruses require their own supply of certain enzymes is because host cells lack enzymes that can replicate the viral genome.

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Key Concepts

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

RNA Virus Replication

RNA viruses need specific enzymes to replicate their genomes because their genetic material is RNA, not DNA. Host cells typically lack the necessary enzymes to replicate RNA directly, as they are equipped to replicate DNA. Therefore, RNA viruses must carry or synthesize their own RNA-dependent RNA polymerase to ensure successful replication within the host.
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Host Cell Enzymatic Limitations

Host cells are generally equipped with enzymes that replicate DNA and transcribe it into RNA, but they do not possess enzymes that can directly replicate RNA genomes. This limitation necessitates that RNA viruses bring their own replication machinery, as the host's cellular machinery cannot fulfill this role, highlighting the need for viral-specific enzymes.
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Viral Enzymes and Protein Synthesis

While host cells have the machinery to translate mRNA into proteins, RNA viruses often encode their own enzymes to ensure efficient translation and processing of viral proteins. These enzymes can modify host cell processes to favor viral protein synthesis, ensuring the virus can replicate and assemble new viral particles effectively within the host.
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Related Practice
Textbook Question

To cause a human pandemic, the H5N1 avian flu virus would have to

a. Spread to primates such as chimpanzees.

b. Develop into a virus with a different host range.

c. Become capable of human-to-human transmission.

d. Become much more pathogenic.

Textbook Question

A bacterium is infected with an experimentally constructed bacteriophage composed of the T2 phage protein coat and T4 phage DNA. The new phages produced would have

a. T2 protein and T4 DNA.

b. T4 protein and T2 DNA.

c. T2 protein and T2 DNA.

d. T4 protein and T4 DNA.

Textbook Question

Emerging viruses arise by

a. Mutation of existing viruses.

b. The spread of existing viruses to new host species.

c. The spread of existing viruses more widely within their host species.

d. All of the above.

Textbook Question

Redraw Figure 19.8 to show the replicative cycle of a virus with a single-stranded genome that can function as mRNA (a class IV virus).