Viral Structure and Multiplication Lecture Notes

These vocabulary flashcards cover the fundamental concepts of viral structure, classification, multiplication cycles, cultivation methods, and noncellular infectious agents such as prions and viroids based on Chapter 5 lecture materials.

Virus

Derived from the Latin word for "poison," these agents infect every type of cell including bacteria, algae, fungi, protozoa, plants, and animals.

Filterable virus

A term established when early researchers found that fluid from host organisms remained infectious even after passing through porcelain filters designed to trap bacteria.

Obligate intracellular parasites

Description for viruses because they cannot multiply unless they invade a specific host cell and instruct its genetic and metabolic machinery to make and release new viruses.

Ultramicroscopic size

The range of most viruses, which typically measure from $20\,\text{nm}$ up to $1,000\,\text{nm}$ in diameter.

Capsid

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

Nucleocapsid

The collective term for the viral capsid and the nucleic acid it contains.

Naked viruses

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

Envelope

An external covering of a capsid, usually composed of a modified piece of the host’s cell membrane.

Spikes

Viral surface proteins that project from the nucleocapsid or envelope, allowing viruses to dock with host cells.

Virion

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

Capsomeres

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

Helical capsid

A structure with rod-shaped capsomeres that bond together to form a series of hollow discs resembling a bracelet, eventually forming a continuous helix.

Icosahedral capsid

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

Complex capsids

Non-symmetrical structures found only in viruses that infect bacteria; they may contain multiple protein types and are never enveloped.

Genome

The sum total of the genetic information carried by an organism; viruses carry either DNA or RNA, but not both.

Positive-sense RNA

Single-stranded viral RNA that is ready for immediate translation by the host cell.

Negative-sense RNA

Single-stranded viral RNA that must be converted before translation can occur.

Segmented RNA

A viral genome where individual genes exist on separate pieces of RNA.

Retroviruses

A special type of RNA virus that carries its own enzymes to create DNA out of its RNA genome.

Polymerases

Enzymes that synthesize DNA and RNA.

Replicases

Enzymes used by viruses to copy RNA.

Reverse transcriptase

An enzyme that synthesizes DNA from an RNA template.

Adsorption

The first phase of the animal viral life cycle where a virus makes an exact fit with a specific host molecule.

Host range

The limited range of cells that a specific virus is capable of infecting.

Tropisms

The specificities of viruses for certain tissues based on compatible receptors.

Endocytosis

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

Fusion

A penetration method where the viral envelope merges directly with the host cell membrane, liberating the nucleocapsid into the cell interior.

Cytopathic effects (CPEs)

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

Inclusion bodies

Compacted masses of viruses or damaged cell organelles found in the nucleus and cytoplasm of infected cells.

Syncytia

The fusion of multiple damaged host cells into single large cells containing multiple nuclei, also known as giant cells.

Provirus

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

Chronic latent state

A condition where viruses remain in a host for long periods and periodically become activated under various stimuli, such as Herpes simplex.

Transformation

The effect of oncogenic viruses on a cell, leading to an increased growth rate and the capacity to divide indefinitely.

Oncoviruses

Mammalian viruses capable of initiating tumors, such as papillomaviruses and hepatitis B virus.

Bacteriophage

A virus that specifically infects bacteria; the name literally means "bacteria eating."

Lytic cycle

The bacteriophage life cycle that ends with the host cell bursting (lysis) to release new virions.

Prophage

An inactive state where viral DNA is inserted into the bacterial chromosome.

Lysogeny

A condition in which the host bacterial chromosome carries bacteriophage DNA and replicates it during normal cell division.

Induction

The process where a prophage in a lysogenic cell becomes activated and progresses directly into viral replication and the lytic cycle.

Lysogenic conversion

When a bacterium acquires a new trait, such as the production of a toxin, from its temperate phage.

In vivo

Viral cultivation methods using laboratory-bred animals and embryonic bird tissues.

In vitro

Viral cultivation methods using cell or tissue culture techniques.

Plaques

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

Antigenic shift

A major genetic reassortment in viruses like Influenza that results from two different viruses infecting the same cell and swapping segments.

Antigenic drift

A process of genetic mutation in the HA gene of the Influenza virus that changes the shape of the antigen so antibodies no longer recognize it.

Prions

Noncellular infectious agents composed primarily of protein with no nucleic acid, responsible for diseases like Creutzfeldt-Jakob disease.

Satellite viruses

Defective virus-like agents that are dependent on other "helper" viruses for replication.

Viroids

Plant pathogens that are about one-tenth the size of an average virus and composed of naked strands of RNA without a capsid.