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) virus b. bluetongue (dsRNA) virus c. measles ([−]ssRNA) virus d. human immunodeficiency (RNA reverse-transcribing) virus

Verified step by step guidance

1. Identify the type of RNA each virus contains. Pea mosaic virus has positive-sense single-stranded RNA ([+]ssRNA), bluetongue virus has double-stranded RNA (dsRNA), measles virus has negative-sense single-stranded RNA ([−]ssRNA), and human immunodeficiency virus is an RNA reverse-transcribing virus.
2. Understand the replication process for each type of RNA. Positive-sense RNA ([+]ssRNA) can be directly translated into viral proteins by the host's ribosomes. Double-stranded RNA (dsRNA) and negative-sense RNA ([−]ssRNA) require their own RNA-dependent RNA polymerase to first create a positive-sense RNA strand that can be translated.
3. Recognize that RNA reverse-transcribing viruses, like the human immunodeficiency virus, first need to reverse transcribe their RNA into DNA, which then integrates into the host's genome and is transcribed back into RNA before translation.
4. Conclude that the pea mosaic virus ([+]ssRNA) can directly make viral proteins when its genome is injected into a host cell because its RNA can be immediately translated by the host's ribosomes.
5. Determine that the bluetongue (dsRNA) virus, measles ([−]ssRNA) virus, and human immunodeficiency (RNA reverse-transcribing) virus cannot make viral proteins directly from just their genomes being injected into a host cell, as they require additional processes or enzymes not provided by the host cell alone.

Key Concepts

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 for protein synthesis, while [−]ssRNA viruses require conversion to [+]ssRNA first.

Host Cell Machinery

Once a virus injects its genome into a host cell, it relies on the host's cellular machinery to replicate and produce viral proteins. This includes ribosomes for translation and enzymes for replication. Understanding how different viral genomes interact with host cell processes is crucial for predicting which viruses can produce proteins directly from their genomes.

Viral Protein Synthesis Mechanisms

Viral protein synthesis mechanisms vary based on the type of viral genome. [+]ssRNA viruses can immediately use their genome as mRNA, while dsRNA viruses must first transcribe their genome into mRNA. In contrast, [−]ssRNA viruses need to be converted to [+]ssRNA before translation can occur. This distinction is essential for predicting which viruses can synthesize proteins upon genome injection.