Difference between the picornavirus and togaviruses genomes?
The correct answer and explanation is:
Picornaviruses and togaviruses are two distinct families of viruses that have differences in their genomic structures. Here’s a breakdown of the differences:
1. Genome Structure:
- Picornaviruses have a single-stranded RNA genome, which is positive-sense. The genome is around 7,000 to 8,500 nucleotides long. It is non-enveloped, and the RNA acts directly as mRNA for translation into proteins once inside the host cell. The genome encodes a single polyprotein that is later cleaved into functional viral proteins.
- Togaviruses also have a positive-sense, single-stranded RNA genome. However, their genome is typically around 10,000 to 12,000 nucleotides long. Togaviruses have an envelope, which makes them different from picornaviruses. The genome is also translated into a single polyprotein, but in some cases, the genome can also be divided into two parts, one for structural proteins and the other for non-structural proteins.
2. Viral Envelopes:
- Picornaviruses are non-enveloped, meaning they lack a lipid membrane surrounding their capsid. This makes them more resistant to environmental factors like temperature, pH, and detergents.
- Togaviruses, in contrast, are enveloped. This lipid membrane is derived from the host cell membrane and makes the virus more sensitive to environmental stress, such as changes in temperature and desiccation.
3. Transmission:
- Picornaviruses include important viruses like poliovirus, rhinovirus, and enterovirus. They are typically transmitted via the fecal-oral route or respiratory droplets.
- Togaviruses include viruses like the rubella virus and the alphavirus group (such as the chikungunya virus). They are often transmitted by arthropod vectors, like mosquitoes.
4. Replication Mechanism:
- Both families replicate their RNA genomes in the host cell cytoplasm. However, togaviruses have a more complex replication cycle, including the synthesis of a subgenomic RNA, which allows for the production of structural proteins.
In summary, while both families of viruses have positive-sense RNA genomes, they differ significantly in their genomic length, envelope presence, transmission modes, and replication mechanisms.