Viruses: Structure, Classification, and Replication Strategies

What is a virus?

Viruses are subcellular biological mechanisms that require the replication machinery of a host cell to replicate themselves.

How many viruses are estimated to exist on the planet?

More than ten million trillion (10^31) viruses.

Do viruses infect all species?

Yes, viruses infect every species that has been examined, including other viruses.

What are individual virus particles called?

Virions.

What is the main role of a virion?

To stabilize genetic material and deliver it to a host cell for replication.

What structures must a virion possess?

Structures to contain and protect genetic material and replication proteins (enzymes), known as the nucleocapsid.

What is a capsid?

A protein structure surrounding the genetic material of a virus, formed by repeating units called capsomers.

What is the relationship between capsomers and nucleocapsid?

Capsomers self-assemble to form the capsid, which combined with the genome forms the nucleocapsid.

What are the two main shapes of capsids?

Icosahedral and helical.

What types of genetic material can viruses contain?

Viruses can contain ssRNA, dsDNA, ssDNA, dsRNA, sense, or antisense genomes.

What is the Baltimore classification?

A system that classifies viruses based on their genome type and the pathways required for replication and transcription.

How many main categories are in the Baltimore classification?

Seven main categories (classes 1-7), with viroids as a potential eighth.

What is a key challenge in classifying viruses?

Classification does not always follow commonly accepted rules and can be difficult.

What is the primary function of a virus?

To protect and deliver its genetic material to host cells for replication.

What is the significance of viral genome size?

There is a compromise between function and size; too small cannot code for necessary functions, too big cannot rely on intracellular existence.

What is the role of specific surface structures in viruses?

They allow binding to and entrance of the host cell.

What defines the efficiency of capsid formation?

The ability of capsomers to self-assemble, minimizing the genetic coding required.

What does the term 'obligate intracellular existence' refer to?

The requirement of viruses to replicate within a host cell.

What is the impact of viruses on host cells?

The impact varies with the species of host and virus; obvious signs of disease do not occur in most cases.

What is the general structure of a virus?

Composed of genetic material (DNA or RNA) enclosed within a protein capsid, often surrounded by additional lipid and sugar layers.

What is a virion's main function?

Genomic replication, dictated by the type of genome present.

What is a challenge in determining if viruses are alive or dead?

Viruses evolve rapidly, complicating the classification of viral species and sub-species.