Final answer:
It is true that certain RNA viruses use their RNA genome as if it were mRNA, allowing host ribosomes to synthesize viral proteins. Viral enzymes and those of the host then process these proteins. Retroviruses, a subset of RNA viruses, require reverse transcription to convert their RNA genome into DNA before protein synthesis.
Step-by-step explanation:
Some viruses indeed use their RNA genome as a giant mRNA, and host ribosomes synthesize an enormous peptide that is then cleaved or processed by both host and viral encoded enzymes to form the proper polypeptides. This is true for certain RNA viruses. As an example, when a virus with a positive single-strand RNA (+ssRNA) genome infects a cell, this viral genomic RNA can act directly as mRNA. The host cell's ribosomes will translate this RNA into a large polypeptide, which is then processed into functional viral proteins by host and viral enzymes. Retroviruses, such as HIV, also use their RNA genome to produce viral proteins, but they do so via a DNA intermediate synthesized by the viral enzyme reverse transcriptase.
The different replication mechanisms of viruses, whether they are DNA or RNA viruses, depend on the structure of their genome. For RNA viruses, their genomic material can serve as a template for the synthesis of viral proteins, essential for forming new virions. However, in the case of retroviruses, they must undergo a unique process where their RNA is reverse transcribed to form DNA, which then integrates into the host genome. This reverse transcription is facilitated by reverse transcriptase, an enzyme provided by the virus, which is a characteristic feature not found in uninfected host cells.