Chapter 6: Viruses Lecture Flashcards

Vocabulary-style flashcards covering the discovery, structure, life cycles, and classification of viruses and other noncellular infectious agents based on the Ch 6 lecture notes.

Virus (Etymology)

Derived from the Latin word for poison; a term coined by Pasteur because he could not grow the agent like bacteria.

Ivanovski and Beijernick

Scientists who discovered that tobacco disease was caused by a filterable agent, proving the existence of viruses.

Loeffler and Frosch

Researchers who identified foot-and-mouth disease as the first animal disease caused by a virus.

Filterable Virus

An infectious agent small enough to pass through porcelain filters designed to trap bacteria, leaving the cell-free filtered fluid infectious.

Obligate Intracellular Parasites

A property of viruses meaning they can only be active and multiply inside host cells (bacteria, protozoa, fungi, algae, plants, and animals).

Viral Size Range

Ultramicroscopic particles ranging from $20\,nm$ to $1000\,nm$ in diameter.

Capsid

A protein shell that surrounds the nucleic acid core of a virus.

Nucleocapsid

The combination of the viral capsid and the nucleic acid it contains.

Envelope

A modified piece of the host cell membrane that surrounds the nucleocapsid in some viruses.

Spikes

Protruding glycoproteins found on naked or enveloped viruses that allow them to dock with host cell receptors.

Virion

A fully formed virus particle that is capable of establishing an infection in a host.

Capsomeres

Identical protein subunits that spontaneously self-assemble to form the viral capsid.

Helical Capsid

A structure consisting of rod-shaped capsomeres that form a continuous helix around the nucleic acid.

Icosahedral Capsid

A three-dimensional, $20$-sided figure with $12$ evenly spaced corners.

Complex Capsids

Non-symmetrical capsids containing multiple types of proteins; found only in bacteriophages.

Genome

The full complement of DNA and RNA carried by a cell; viruses contain either DNA or RNA, but never both.

Positive-sense RNA

Single-stranded RNA genomes that are ready for immediate translation into proteins.

Negative-sense RNA

RNA genomes that must be converted into the proper form before they can be translated into proteins.

Polymerases

Viral enzymes responsible for synthesizing DNA and RNA.

Reverse Transcriptase

An enzyme used by viruses like HIV to synthesize DNA from an RNA template.

Adsorption

The process where a virus attaches specifically to receptor sites on the host cell membrane.

Host Range

The limitation of a virus to invade only specific host cells based on the exact fit with host molecules.

Endocytosis

A penetration method where the entire virus is engulfed by the cell and enclosed in a vacuole or vesicle.

Uncoating

The process where enzymes in a vacuole dissolve the viral envelope and capsid to release the nucleic acid into the cytoplasm.

Cytopathic Effects (CPEs)

Virus-induced damage to the host cell that alters its microscopic appearance, such as changes in size, shape, or intracellular damage.

Inclusion Bodies

Compacted masses of viruses or damaged cell organelles found in the nucleus or cytoplasm; example: Negri bodies in rabies.

Syncytia

The fusion of multiple host cells into single large cells containing multiple nuclei, commonly caused by herpes viruses.

Provirus

Viral DNA that has been incorporated into the DNA of the host cell.

Chronic Latent State

A persistent infection where the virus remains inactive for periods followed by periodic reactivation (e.g., Herpes simplex).

Oncogenic Viruses

Viruses experts estimate are responsible for up to $13\%$ of human cancers.

Bacteriophage

Viruses that parasitize bacteria; often make their bacterial hosts more pathogenic for humans.

Lytic Cycle

A bacteriophage life cycle that ends with the destruction (lysis) of the bacterial host cell.

Lysogeny

A condition where the viral DNA (prophage) is inserted into the bacterial chromosome and duplicated along with the host genome.

Induction

The activation of a prophage in a lysogenic cell to progress into viral replication and the lytic cycle.

Lysogenic Conversion

The acquisition of new traits, such as toxins (diphtheria, cholera, or botulism), by a bacterium from a temperate phage.

In vivo

Viral cultivation methods using living embryos or laboratory animals like white mice and rabbits.

In vitro

Viral cultivation methods using cell or tissue cultures in sterile dishes or bottles.

Plaques

Clear, well-defined patches in a cell sheet where virus-infected cells have been destroyed.

Interferon (IFN)

A naturally occurring human cell product used to prevent and treat some viral infections.

Prions

Proteinaceous infectious particles that cause fatal neurodegenerative diseases (spongiform encephalopathies) and lack nucleic acids.

Viroids

Plant pathogens composed only of naked strands of RNA, lacking a capsid or coating.