Microbiology: Viruses and Prions

Comprehensive vocabulary flashcards covering the characteristics, structure, replication, and clinical aspects of viruses and prions based on the Microbiology lecture notes.

Virology

The study of viruses.

Virion

A single, infectious virus particle with an exterior protective protein capsid and genetic material consisting of DNA or RNA.

Capsid

The protein shell that packages and protects the viral genome; it accounts for the bulk of a virion's mass.

Capsomere

The individual protein subunits that make up the viral capsid.

Helical capsid

A capsid structure that looks like a hollow tube.

Icosahedral capsid

A capsid structure that looks like three-dimensional polygons.

Complex capsids

Structural deviations from helical or icosahedral forms; often seen in bacteriophages which use additional structures to inject their genome into target cells.

Bacteriophages

Also known as phages; these are viruses that infect bacteria.

Enveloped viruses

Viruses that have a lipid-based envelope surrounding the capsid, which arises from budding off the host cell membrane.

Naked viruses

Also known as nonenveloped viruses; they lack an envelope and usually arise from lysing (bursting) the host cell.

Spikes

Also called peplomers; these are protein structures that protrude from the viral capsid or envelope and help the virus attach to and enter host cells.

Hemagglutinin (HA)

A specific type of spike protein found on Influenza A viruses used for identification by the host immune system.

Neuraminidase (NA)

A specific type of spike protein found on Influenza A viruses involved in viral evolution and immune recognition.

RNA-dependent RNA polymerases (RdRPs)

Specialized enzymes used by negative single-stranded RNA viruses to transcribe their genome into mRNA.

Reverse transcriptase

An enzyme used by retroviruses to convert their RNA genome into DNA prior to insertion into the host DNA.

Antigenic drift

Minor genetic changes in a virus (such as influenza) resulting from frequent mutations in its RNA genome, causing small changes in spike proteins.

Antigenic shift

A major genetic reassortment that can occur when two different viral strains coinfect a single host cell, potentially leading to a pandemic.

Attenuated strains

Viral strains that have undergone genetic changes that limit their infectivity; these are often used in vaccines.

Tropism

Refers to the tissue or cell specificity of a virus, determined by viral surface factors.

Host range

The collection of species that a virus is capable of infecting.

Lytic replication pathway

A bacteriophage replication pathway where the virus infects the host, builds new virions, and kills the host cell upon release.

Lysogenic replication

A replication pathway in temperate phages where the viral genome is incorporated into the host cell genome.

Prophage

The phage genome when it is integrated into the host bacterial cell genome.

Phage conversion

The process by which prophages confer new pathogenic properties, such as toxins, to bacterial cells.

Uncoating

A step in animal virus replication where the capsid is digested by enzymes in the endocytic vesicle, cytoplasm, or nucleus to release the genome.

Chronic persistent infections

Infections characterized by the continuous release of virions over a long period and a slow progression of disease.

Provirus

The state of a viral genome (such as HIV) when it has integrated into the host cell DNA.

Latent persistent infections

Infections characterized by intermittent flare-ups of symptoms and virion shedding separated by periods of dormancy.

Oncogenic viruses

Viruses that cause cancer by stimulating uncontrolled host cell division or decreasing host cell responsiveness to death signals.

Plaque

A clear zone on a bacterial lawn where host cells have been lysed by bacteriophages.

Plaque-forming units (PFUs)

A measurement of the quantity of bacteriophages in an initial volume of sample.

Viral titer

The quantity of virus present in a given volume of sample.

Specificity

The property of a diagnostic test to detect only the virus of interest without giving false positives.

Sensitivity

The property of a diagnostic test to detect very low levels of the target without giving false negatives.

Agglutination tests

Diagnostic tests using purified antibodies linked to latex beads that clump together in the presence of a specific viral antigen.

ELISA

Enzyme-linked immunosorbent assay; a diagnostic tool that uses color changes to detect the presence of either antigens or antibodies.

Seroconversion window

The time period it takes for a patient to build up detectable levels of antibodies against a virus.

Nucleoside analogs

A class of antiviral drugs that mimic normal nucleotides to block viral replication by acting as a chemical dead end.

Interferons

Naturally occurring substances released by cells in response to viral infection that signal neighboring cells to make defensive changes.

Prions

Infectious proteins that do not contain genetic material and cause transmissible spongiform encephalopathies ($TSEs$).

Smallest virus size

Approximately $30\,nm$ (e.g., rhinoviruses and polioviruses).

Largest virus size

Approximately $1,500\,nm$ in length (e.g., Pithovirus).