RNA Viruses

Viral genomes may be encoded in either DNA or RNA. Some medically important human viruses have RNA as their genetic material, including those that cause influenza, common colds, polio, and AIDS. Almost all viruses that infect plants have RNA genomes. The medical and economic importance of RNA viruses has encouraged their study.

RNA viruses, like bacteriophages, reproduce by infecting cells and making copies of themselves. Most use RNA-dependent RNA polymerases encoded by their own genes.

In positive-strand RNA viruses, the genomic RNA molecule carried inside the viral particle codes directly for viral proteins ( FIGURE 8.34a). In negative-strand RNA viruses, the virus first makes a complementary copy of its RNA genome, which is then translated into viral proteins (< Figure 8.34b).

Positive-strand RNA codes directly for coat proteins.

The other RNA strand is synthesized.

Negative-strand RNA is copied into complementary RNA...

Positive-strand RNA codes directly for coat proteins.

-Polypeptide

The other RNA strand is synthesized.

Negative-strand RNA is copied into complementary RNA...

^-Ribosome

Viral protein

RNA is replicated

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