Textbook Question
Compare and contrast the bacteriophage lytic cycle and lysogeny by addressing
(1) the rate of replication of the viral genome
(2) production of virions, and
(3) effect on the host cell.
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17. Viruses
Viruses
1:36 minutesProblem 8
Textbook Question
Of the viruses highlighted in Section 33.4, predict which of the following would be able to make viral proteins if nothing more than its genome were injected into a suitable host cell.a. pea mosaic ([+]ssRNA) virusb. bluetongue (dsRNA) virusc. measles ([−]ssRNA) virusd. human immunodeficiency (RNA reverse-transcribing) virus
Verified step by step guidance1
Identify the type of RNA each virus contains and understand the implications for protein synthesis. Positive-sense single-stranded RNA ([+]ssRNA) can be directly translated into proteins by the host's ribosomes. Double-stranded RNA (dsRNA) and negative-sense single-stranded RNA ([−]ssRNA) require transcription into a positive-sense RNA before translation can occur. RNA reverse-transcribing viruses need to reverse transcribe their RNA into DNA, which then needs to be transcribed into mRNA.
Analyze the pea mosaic virus, which has a [+]ssRNA genome. Since [+]ssRNA can act as mRNA, this virus can directly make viral proteins using the host's ribosomes once its genome is injected into the cell.
Consider the bluetongue virus with a dsRNA genome. This type of RNA cannot be directly translated into proteins. The virus must first use its own RNA-dependent RNA polymerase to transcribe the dsRNA into positive-sense mRNA, which is not possible if only the genome is injected without the necessary viral enzymes.
Evaluate the measles virus, which contains a [−]ssRNA genome. Similar to dsRNA viruses, [−]ssRNA cannot be directly translated into proteins. It requires transcription into a complementary [+]ssRNA by viral RNA-dependent RNA polymerase, which must be present in the virion or in the host cell.
Assess the human immunodeficiency virus, an RNA reverse-transcribing virus. This virus must first reverse transcribe its RNA into DNA, which then needs to be integrated into the host's genome and transcribed into mRNA. This process requires viral reverse transcriptase and integrase enzymes, which are not available if only the genome is injected.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Viral Genome Types
Viruses can have different types of genomes, including single-stranded RNA ([+]ssRNA, [−]ssRNA), double-stranded RNA (dsRNA), and reverse-transcribing RNA. The type of genome influences how the virus replicates and produces proteins within a host cell. For instance, [+]ssRNA viruses can directly serve as mRNA, while [−]ssRNA viruses require conversion to [+]ssRNA before translation.
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Viral Protein Synthesis
Viral protein synthesis occurs when a virus hijacks a host cell's machinery to produce its proteins. This process depends on the viral genome type; [+]ssRNA can be translated directly, while dsRNA and [−]ssRNA require additional steps. Understanding these mechanisms is crucial for predicting which viruses can produce proteins from just their genome.
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Host Cell Compatibility
The ability of a virus to produce proteins is also contingent on the compatibility of its genome with the host cell's translation machinery. Different host cells may have varying capabilities to recognize and translate viral RNA, affecting the virus's ability to replicate and express its proteins. This concept is essential for determining which viruses can function effectively in a given host.
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