Viruses, Viroids, and Prions Practice Flashcards

This set of flashcards covers vocabulary and key concepts from Chapter 6, including virus structure, multiplication cycles, bacteriophages, and other infectious agents like prions and viroids.

Obligate intracellular parasites

A property of viruses meaning they must reside inside bacteria, protists, fungi, plants, or animals to function and replicate.

Ultramicroscopic

The general size of most viruses, which is typically <0.2\,\mu m and requires an electron microscope to view.

Capsid

A protein shell that encloses and protects the nucleic acid core of all viruses.

Nucleocapsid

The combined structure of the viral protein coat (capsid) and the nucleic acid it surrounds.

Envelope

An external covering, mostly found in animal viruses, acquired when the virus leaves the host cell.

Naked viruses

Viruses that consist only of a nucleocapsid and lack an external envelope.

Capsomers

Identical protein subunits that assemble to form the viral capsid.

Helical Capsid

A structural type where rod-shaped capsomers assemble into hollow discs, forming a continuous cylindrical helix.

Icosahedral Capsid

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

Spikes

Exposed proteins on the outside of the viral envelope that are essential for the virus to attach to the host cell.

Poxviruses

Atypical viruses that lack a typical capsid and are instead covered by a dense layer of lipoproteins and coarse fibrils.

Bacteriophages

Complex viruses that infect bacteria, often possessing a polyhedral nucleocapsid along with a helical tail and attachment fibers.

Positive-sense RNA

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

Negative-sense RNA

Single-stranded RNA (ssRNA) genomes that must be converted into a proper form before they can be translated.

Polymerases

Pre-formed enzymes carried by viruses that are required to synthesize DNA or RNA during replication.

Reverse transcriptase

An enzyme used by the HIV virus to synthesize DNA from an RNA template.

Adsorption

The phase of the viral multiplication cycle where the virus binds specifically to receptor sites on the host cell membrane.

Host range

The specific spectrum of cells a virus can infect, such as Hepatitis B infecting only human liver cells.

Uncoating

The step in animal virus multiplication where the viral nucleic acid is released from its capsid after entering the host cell.

Budding

A release method for enveloped viruses where the nucleocapsid binds to the membrane, which then pinches off to shed the viruses gradually.

Cell lysis

The rupturing of a host cell to release nonenveloped or complex viruses, usually resulting in the immediate death of the cell.

Cytopathic effects

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

Persistent infections

Infections where the cell harbors the virus and is not immediately lysed, potentially lasting for the host's lifetime.

Chronic latent state

A condition in which a persistent virus periodically reactivates, as seen with Herpes simplex and Herpes zoster viruses.

Transformation

The effect on a host cell when an oncogenic virus permanently alters its genetic material, leading to increased growth and potential tumor formation.

Oncoviruses

Mammalian viruses capable of initiating tumors, such as Papillomavirus and Epstein-Barr virus.

Lytic cycle

The process of bacteriophage multiplication that ends with the release of new viruses through cell lysis induced by viral enzymes.

Lysogenic conversion

A process where phage genes in a bacterial chromosome cause the production of toxins or enzymes that result in pathology, such as in Vibrio cholerae.

Prions

Misfolded proteins that contain no nucleic acid and cause fatal neurodegenerative diseases like Creutzfeldt-Jakob Syndrome (CJS).

Viroids

Noncellular infectious agents comprised of short pieces of RNA without a protein coat, solely identified in plants.