Virology Principles and Classification

A set of vocabulary flashcards detailing viral history, structure, host interactions, genomic properties, and classification systems based on the lecture notes.

Chamberland-Pasteur filter

A filter used to remove all microscope-visible bacteria from a liquid, which led to the discovery of viruses when Ivanowski's filtered extract in 1892 still transmitted tobacco mosaic disease.

Virion size range

The typical size of virions, measured at $20\text{--}250\text{ nm}$, which is below the resolution limit of light microscopes and necessitates electron microscopy for visualization.

Scanning electron microscopy (SEM)

An imaging technique that shows only the surface structure of a virion.

Transmission electron microscopy (TEM)

The only imaging technique capable of showing the internal structure of a virion.

Regressive hypothesis

A viral origin hypothesis proposing that viruses evolved from free-living cells or intracellular parasites that shrank down over time.

Progressive hypothesis

Also known as the escapist hypothesis, this viral origin hypothesis proposes that genetic elements like transposons escaped out of cells and gained the ability to re-enter other cells.

Virus first hypothesis

A viral origin hypothesis proposing that viruses predated cellular life entirely.

Capsid

The complete protein coat surrounding a virion's nucleic acid core.

Capsomere

Individual protein subunits encoded by the viral genome that assemble into the capsid.

Envelope

An optional membrane surrounding a virion that is derived from the host cell rather than built by the virus, making enveloped viruses more fragile to heat, pH shifts, and disinfectants.

CD4

A host cell adhesion molecule that keeps immune cells in proximity during a T lymphocyte response, which HIV evolved to exploit as an attachment receptor.

Matrix proteins

Internal proteins located just inside the envelope of viruses like influenza that stabilize virion shape and assist in progeny assembly.

Segmented genome

A viral genome divided into multiple distinct pieces rather than one continuous strand, which drives high variability and continuous evolution in viruses like influenza.

Baltimore system

A viral classification system organized around how each virus produces mRNA during replication, which provides a unified functional basis common to all viruses.

Positive polarity (ssRNA)

Viral single-stranded RNA genomes in Group IV that read and function directly as mRNA.

Negative polarity (ssRNA)

Viral single-stranded RNA genomes in Group V that are complementary to mRNA and must be transcribed before translation can occur.

Group VI viruses

Viruses such as HIV that start with an ssRNA genome, use reverse transcriptase to form dsDNA, and integrate into the host genome.

Group VII viruses

Viruses such as hepatitis B that start with a partial dsDNA genome and replicate through an RNA intermediate that reverse transcriptase converts back into DNA.