Microbiology Chapter 6: Viruses, Viroids, and Prions

Comprehensive vocabulary flashcards generated from lecture notes covering viral structure, classification, multiplication cycles, bacteriophages, lysogeny, prions, and viroids.

Viruses

Noncellular particles with a definite size, shape, and chemical composition that act as obligate intracellular parasites.

Louis Pasteur

Scientist who postulated in 1884 that rabies was caused by a "living thing" smaller than bacteria.

Dmitri Ivanovski

Scientist who first proposed the term "virus" (from the Latin word for "poison").

Obligate Intracellular Parasites

Organisms that cannot multiply independently and must take control of a host cell's genetic material and metabolic machinery to synthesize new viruses.

Capsid

The protective protein shell that encloses the viral nucleic acid core.

Capsomeres

Identical protein subunits that construct the viral capsid.

Nucleocapsid

The combined viral structure consisting of the protein capsid together with its enclosed nucleic acid core.

Envelope

An external lipid layer surrounding the capsid in some viruses, acquired when the virus leaves the host cell.

Naked Virus

A virus that lacks an external envelope, consisting only of a nucleocapsid.

Helical Capsid

A capsid structure formed by a continuous helix of capsomers creating a cylindrical nucleocapsid.

Icosahedral Capsid

A three-dimensional, symmetrical polygon capsid with 20 sides and 12 evenly spaced corners.

Spikes

Exposed proteins on the surface of the viral envelope or capsid that are essential for attaching the virus to specific host cell receptors.

Complex Viruses

Atypical viruses with non-standard structures, such as poxviruses (covered by lipoproteins and lacking a typical capsid) or bacteriophages (polyhedral head with a helical tail).

Positive-Sense RNA

Single-stranded viral RNA genomes that match mRNA and are ready for immediate translation into proteins by host cell ribosomes.

Negative-Sense RNA

Single-stranded viral RNA genomes that must be converted into positive-sense RNA by viral RNA polymerase prior to translation.

Reverse Transcriptase

A pre-formed viral enzyme carried by viruses such as HIV that synthesizes DNA from an RNA template.

Viral Species

Distinct virus types that share a collection of properties such as host range, pathogenicity, and genetic makeup.

Adsorption (Attachment)

The first step in viral multiplication, involving specific binding between viral surface molecules and receptors on the host cell membrane.

Penetration (Entry)

The step in the viral multiplication cycle where the viral genome or the entire virus enters the host cell.

Uncoating

The process during viral entry where the viral capsid (and vesicle or envelope) breaks down, releasing the viral nucleic acid into the cytoplasm.

Synthesis (Replication)

The viral multiplication phase where the cell synthesizes viral nucleic acids, capsomers, spikes, and enzymes under viral genetic control.

Assembly

The multiplication phase where manufactured capsomers, nucleic acids, and viral spikes are put together to construct mature virions.

Release

The final phase of viral multiplication where complete viral particles exit the host cell via exocytosis (budding) or cell lysis.

Host Range

The specific spectrum of host cells and tissues that a particular virus can infect based on exact receptor binding.

Endocytosis

A mode of viral entry where the host cell membrane engulfs the entire naked or enveloped virus within a vacuole or vesicle.

Fusion

A mode of entry unique to enveloped viruses where the viral membrane fuses directly with the host cell membrane to release the nucleocapsid.

Budding (Exocytosis)

A release process in enveloped viruses where the nucleocapsid binds to the host membrane and pinches off gradually without immediately killing the cell.

Cell Lysis

A release mechanism in nonenveloped and complex viruses where the host cell ruptures and dies, suddenly releasing virions.

Cytopathic Effects (CPEs)

Virus-induced damage to host cells that alters their microscopic appearance, including cell shape changes, inclusion bodies, or cell fusion.

Syncytium

A multinucleated giant cell formed when viral infection causes adjacent host cell membranes to fuse together.

Negri Bodies

Cytoplasmic inclusion bodies found in cells infected by the Rabies virus.

Persistent Infections

Infections where the host cell harbors the virus without immediate lysis, lasting weeks, years, or the host's lifetime.

Chronic Latent State

A persistent infection state where a virus remains hidden or inactive inside host cells for long periods and periodically reactivates.

Transformation

The process by which an oncogenic virus permanently alters a host cell's genetic material, causing uncontrolled cell division and cancer.

Oncoviruses

Mammalian viruses capable of initiating tumors or cancer in host tissues.

Bacteriophages

Viruses that specifically target and infect bacterial cells.

Lytic Cycle

A bacteriophage multiplication path that completes viral assembly and causes destruction and lysis of the bacterial host cell.

Lysogeny

A state where a temperate bacteriophage genome integrates into the bacterial chromosome and persists without causing immediate host cell lysis.

Temperate Phages

DNA bacteriophages that undergo adsorption and penetration but enter lysogeny instead of immediately executing the lytic cycle.

Prophage

An inactive viral genome integrated directly into specific sites on a bacterial host chromosome during lysogeny.

Lysogenic Conversion

The acquisition of new traits or pathology (such as bacterial toxin production) by host bacteria due to carrying genes within a prophage.

Induction

The activation of a dormant lysogenic prophage, causing it to separate from the bacterial chromosome and re-enter the lytic cycle.

In Vitro Cultivation

Cultivating viruses in artificial environments outside a living organism, such as in cell or tissue cultures (e.g., HeLa cells).

In Vivo Cultivation

Propagating viruses within intact living organisms, such as bird embryos or laboratory animals.

Oncolytic Viruses

Attenuated or genetically engineered viruses that selectively target, infect, and destroy cancer cells while sparing normal tissue.

Prions

Infectious misfolded protein particles containing no nucleic acids that cause transmissible spongiform encephalopathies.

Transmissible Spongiform Encephalopathies (TSEs)

Fatal neurodegenerative diseases caused by prions in humans and animals, resulting in sponge-like brain tissue degeneration.

Satellite Viruses

Noncellular infectious particles that are dependent on co-infection with other helper viruses to replicate.

Viroids

Infectious agents consisting of short, naked strands of RNA lacking a protein coat, found only in plants.