Viral Structures & Functions Flashcards

Vocabulary terms and definitions compiled from the lecture on viral structures, taxonomy, and multiplication cycles.

Viruses

Obligate intracellular parasites that are simple, acellular, and do not meet the criteria to qualify as alive.

Bacteriophage

A virus that infects prokaryotic cells, often possessing a complex symmetry with an icosahedral head and a helical tail.

Capsid

A protein coat that encloses and protects the viral nucleic acid; it is composed of identical protein subunits called capsomers.

Nucleocapsid

The structure formed by the combination of the viral capsid and the nucleic acid it encloses.

Envelope

A lipid bilayer external covering found mostly in animal viruses, acquired when the virus leaves the host cell.

Naked Viruses

Viruses that lack an external envelope and consists only of a nucleocapsid.

Spikes

Exposed proteins on the outside of the viral envelope that are essential for the attachment of the virus to the host cell.

General size of most viruses

Most viruses are less than $0.2\,\mu m$ and require an electron microscope for visualization.

Icosahedral Symmetry

A capsid structure composed of equilateral triangles, found in viruses such as Poliovirus, Rhinovirus, and Adenovirus.

Helical Symmetry

A capsid structure with a central cavity and disc shapes, exemplified by the Tobacco Mosaic Virus.

Viral Genome

The genetic material of a virus, which can be either DNA or RNA but never both.

Positive-sense RNA

ssRNA genomes that are ready for immediate translation into proteins.

Negative-sense RNA

ssRNA genomes that must be converted into a proper form before they can be translated.

Polymerases

Pre-formed enzymes present in some viruses used to synthesize DNA or RNA.

Reverse transcriptase

An enzyme used by viruses like the AIDS virus to synthesize DNA from an RNA template.

Adsorption

The first phase of animal virus multiplication involving the binding of the virus to specific molecules on the host cell.

Uncoating

The process in the viral multiplication cycle where the viral nucleic acid is released from the capsid.

Release

The final phase of the viral lifecycle where assembled viruses leave the host cell through budding (exocytosis) or cell lysis.

-viridae

The suffix used to denote a viral family name, such as Herpesviridae.

-virus

The suffix used to denote a viral genus name, such as Simplexvirus.

Viral Species

A population of viruses that share a distinct pool of genes.