Ch.13 Viruses, Viroids, and Prions

Comprehensive vocabulary flashcards covering the structure, discovery, morphology, replication, and pathology of viruses and prions based on Chapter 13 lecture notes.

Contagium vivum fluidum

A phrase meaning contagious living fluid, coined by Martinus Beijerinck in 1898 to describe an infectious viral agent that replicates only in living cells.

Adolf Mayer (1886)

The scientist who discovered in 1886 that tobacco mosaic disease was infectious.

Dmitri Ivanovsky (1892)

The scientist who showed in 1892 that the infectious agent of tobacco mosaic disease passed through a bacteria-proof filter.

Martinus Beijerinck (1898)

The scientist who in 1898 coined the term contagium vivum fluidum and proved that the agent replicates only in living cells.

Electron Microscope (1930s)

The microscopy technology developed in the 1930s that allowed viruses to be seen directly for the first time and their sizes to be ascertained.

Viruses

Obligatory intracellular parasites ranging from $20\text{ to }1000\,\text{nm}$ in length that contain either DNA or RNA surrounded by a protein coat, and lack ribosomes and ATP-generating machinery.

Virion

A complete, fully developed viral particle composed of nucleic acid surrounded by a coat.

Viral Nucleic Acid

The viral genome consisting of either DNA or RNA (never both) that may be single- or double-stranded, linear or circular, or divided into several molecules, accounting for $1\%$ to $50\%$ of the virus's total composition relative to protein.

Capsid

The protein coat surrounding the viral nucleic acid, composed of protein subunits termed capsomeres.

Capsomeres

Subunits that assemble to form the viral capsid, which can consist of a single protein type or several different types.

Naked viruses

Viruses (also referred to as nonenveloped viruses) that possess only a nucleic acid and a capsid, lacking a surrounding lipid envelope.

Viral Envelope

An outer membrane enclosing the capsid of certain viruses, composed of lipids, proteins, and carbohydrates.

Spikes

Carbohydrate-protein complexes covering certain viral envelopes used to facilitate attachment to host cells and commonly used to identify influenza viruses.

Helical viruses

Viruses with a morphology characterized by hollow cylinders surrounding the nucleic acid.

Polyhedral viruses

Viruses whose capsids display a many-sided morphology.

Enveloped viruses

Viruses encased in an outer envelope that are roughly spherical in overall shape but highly pleomorphic.

Complex viruses

Viruses that exhibit complicated structures, such as bacteriophages with a polyhedral capsid attached to a helical tail.

Host range

The specific spectrum of host species and cell types that a virus can infect, determined by viral attachment sites and cellular factors.

Fomites

Inanimate objects involved in the indirect contact transmission of viral infections.

Biological vectors

Living vectors, such as mosquitoes, that participate directly in the transmission of a virus.

Mechanical vectors

Living vectors, such as flies, that passively transport viral pathogens without internal biological involvement.

Zoonoses

Infectious diseases transmitted from animals to humans, such as avian influenza.

Reverse zoonoses

Infectious viral transmission occurring from humans to animals.

Antigenic drift

The gradual accumulation of mutations in a virus that leads to localized epidemics.

Antigenic shift

A genetic event where two different viruses mix to form a completely new virus, capable of causing a pandemic.

Attachment

The first stage of viral replication in which viruses bind to the host cell membrane.

Entry

The second phase of viral replication where the virus enters the cell via receptor-mediated endocytosis or fusion.

Uncoating

The process during viral replication where viral or host enzymes break down the capsid to release nucleic acid.

Biosynthesis

The viral replication step dedicated to the cellular production of viral nucleic acid and proteins.

Maturation

The stage of the viral replication cycle where newly synthesized nucleic acid and capsid proteins assemble into complete particles.

Budding

A release mechanism employed by enveloped viruses to exit the host cell while acquiring their lipid envelope.

Oncogenic viruses

Viruses that integrate into host cell DNA, activating proto-oncogenes into oncogenes and causing cellular transformation that leads to uncontrolled growth.

Latent viral infections

Infections where the virus persists inside host cells for prolonged periods without producing an active infection, with examples including cold sores and shingles.

Persistent viral infections

Disease processes that develop gradually as conventional viruses accumulate over a long period, which are generally fatal.

Prions

Proteinaceous infectious particles lacking nucleic acids that misfold and convert normal PrP to abnormal forms, leading to spongiform brain tissue and incurable disease.

Mad Cow Disease (BSE)

A fatal spongiform encephalopathy affecting cattle caused by infectious prions.

Variant CJD

A human prion disease resulting from the consumption of beef infected with Mad Cow Disease (BSE).

Scrapie

A fatal prion-mediated spongiform disease that affects sheep.

Kuru

A historical human prion disease causing spongiform brain tissue degeneration.