Ch 13-Viruses, Viroids, and Prions Flashcards

A Comprehensive collection of vocabulary terms regarding viral structure, replication cycles, taxonomy, clinical infections, and other acellular infectious agents like viroids and prions.

Viruses

Obligate intracellular parasites consisting of genetic information (DNA or RNA) contained within a protective protein coat; they are acellular and not living organisms.

Capsid

The protective protein coat of a virus that surrounds the nucleic acid.

Capsomeres

Individual protein subunits that make up the viral capsid.

Bacteriophages

Viruses that infect bacteria, often used as models for animal virus interaction with hosts; also known as phages.

Megaviridae

A family of the largest viruses, reaching approximately $800\,nm$ in diameter.

Virophage

A virus that is a parasite of another virus, such as Sputnik which is a parasite of Mimivirus.

Virion

A complete viral particle consisting of nucleic acid surrounded by a protein coat (capsid).

Nucleocapsid

The combination of the viral capsid plus the nucleic acids it contains.

Enveloped viruses

Viruses surrounded by a lipid bilayer obtained from the host cell, often with a matrix protein between the nucleocapsid and envelope.

Naked viruses

Non-enveloped viruses that lack a lipid bilayer and are generally more resistant to disinfectants.

Spikes

Structures on the outside of a virion used for attachment to receptor sites on host cells.

Icosahedral

A basic viral shape characterized by 20 flat triangles.

Helical

A basic viral shape where capsomeres are arranged in a helix.

Arboviruses

A group of unrelated viruses spread by arthropods (arthropod-borne) that cause diseases like yellow fever and West Nile encephalitis.

Lytic (virulent) phages

Bacteriophages that exit the host cell by lysing it at the end of a productive infection cycle.

Temperate phages

Phages that can either direct a lytic infection or incorporate their DNA into the host cell genome (lysogenic infection).

Lysogen

A bacterium that is infected with a temperate phage and carries the viral DNA in its genome.

Prophage

The integrated phage DNA within a host cell's chromosome during a lysogenic infection.

Phage induction

The process by which a prophage is excised from the host chromosome (often due to DNA damage) to enter the lytic cycle.

Lysogenic conversion

A change in the phenotype of a lysogen caused by the presence of prophage DNA, such as the production of toxins in Corynebacterium diphtheria.

Generalized transduction

A form of horizontal gene transfer resulting from a packaging error during phage assembly where bacterial DNA is mistakenly packaged into a phage head.

Specialized transduction

A form of horizontal gene transfer resulting from an excision mistake during the transition from the lysogenic to lytic cycle of a temperate phage.

Plaque assays

A method used to count phage particles in samples by observing zones of clearing (plaques) on a bacterial lawn.

Uncoating

The process by which the viral nucleic acid separates from its protein coat after entering an animal host cell.

Polyprotein

A large viral protein that is cleaved by specific proteases into individual functional proteins; a common target for antiviral medications.

Replicase

A virally encoded RNA-dependent RNA polymerase used by RNA viruses to replicate their genomes using an RNA template.

Antigenic drift

The accumulation of mutations in surface proteins of RNA viruses due to the lack of proofreading by replicase, resulting in new viral strains.

Antigenic shift

A major change in a viral subtype resulting from the reassortment of genome segments when two different strains infect the same host cell.

Reverse transcriptase

An enzyme encoded by retroviruses and other reverse-transcribing viruses that synthesizes DNA from an RNA template.

Budding

A process by which most enveloped viruses are released from the host cell, acquiring their lipid envelope and matrix protein as they exit.

Acute infections

Viral infections characterized by a rapid onset of symptoms and a short duration, after which the immune system eliminates the virus.

Persistent infections

Infections that continue for years or a lifetime, which may be either chronic or latent.

Chronic infections

A type of persistent infection characterized by the continuous production of low levels of virus particles, even in the absence of symptoms.

Latent infections

A type of persistent infection where the viral genome (provirus) remains silent in the host cell but can reactivate to cause a productive infection.

Provirus

A silent viral genome that has integrated into an animal host's chromosome or is replicating separately as a plasmid.

Proto-oncogenes

Normal host genes that stimulate cell growth and division; mutations or viral interference can turn them into oncogenes.

Oncogene

A modified proto-oncogene that promotes uncontrolled cell growth, potentially leading to tumor formation.

Cytopathic effects

Distinct morphological alterations in host cells caused by viral replication, such as cell rounding, lysis, or forming syncytia.

Syncytium

A giant multinuclear cell formed by the fusion of multiple host cells due to viral infection.

Viroids

Small, single-stranded RNA molecules that function as plant pathogens and are not classified as viruses.

Prions

Proteinaceous infectious agents composed solely of protein, linked to slow, fatal spongiform encephalopathies.

$$PrP^C$$

The normal, protease-sensitive form of the neuronal prion protein.

$$PrP^{SC}$$

The infectious, protease-resistant, and insoluble form of the prion protein that causes misfolding of normal proteins.