Biological Diversity: Viruses

Vocabulary flashcards summarizing core terms, structures, processes, and defenses related to viruses and viral infections.

Virus

A non-living infectious particle that can infect host cells, replicate inside them, and spread to new cells but lacks independent metabolic activity.

Bacteriophage

A virus that specifically infects bacterial cells, often possessing a sheath and tail fibers for DNA injection and attachment.

Retrovirus

An RNA virus that uses the enzyme reverse transcriptase to make double-stranded DNA from its single-stranded RNA genome.

Reverse Transcriptase

Viral enzyme that synthesizes complementary DNA (cDNA) from an RNA template in retroviruses.

Sheath (of bacteriophage)

Contractile structure that helps eject phage DNA into a bacterial host cell.

Tail Fibers

Phage appendages that recognize and attach to specific receptors on the bacterial surface.

Acute Viral Infection

Infection characterized by rapid onset, high virion replication, and resolution within days.

Chronic Viral Infection

Infection that begins with high viral load followed by reduced but persistent viral levels lasting years to a lifetime.

Latent Viral Infection

Infection with intermittent periods of low and high viral load after an initial acute phase, persisting for years or life.

Slow-Progressing Infection

Infection that appears dormant after initial exposure but exhibits viral replication years later.

Epidemic

Disease outbreak affecting a large population within a specific region.

Pandemic

A global outbreak of a disease affecting populations worldwide.

Vaccine

A weakened or inactivated agent that mimics a pathogen to stimulate an immune response and confer protection.

Viral Genome (Nucleic Acid)

The viral genetic material, which may be double- or single-stranded DNA or RNA.

Prophage

Viral genome integrated into the chromosome of a bacterial host cell.

Provirus

Viral genome integrated into a eukaryotic host’s genome.

Capsid

Protein coat that encloses and protects the viral nucleic acid.

Viral Envelope

Outer lipid membrane derived from host cell membranes and embedded with viral glycoproteins, common in animal viruses.

Antigenic Shift

Major genetic reassortment between viruses that expands host range and complicates treatment.

Antigenic Drift

Minor, gradual mutations in viral genes that allow reinfection of the same host species.

Host Range

The set of species—and in some cases specific tissues—that a virus can infect.

Virion

A fully assembled, infectious viral particle outside the host cell.

Attachment (Adsorption)

Initial binding of viral surface proteins to specific receptors on the host cell membrane.

Entry

Process by which a virus or its genome penetrates the host cell, via injection, membrane fusion, or endocytosis.

Uncoating

Removal or breakdown of the capsid to expose the viral genome inside the host cell.

Synthesis/Replication

Stage where the virus directs host resources to duplicate its genome and synthesize viral proteins.

Self-Assembly

Spontaneous assembly of viral genomes and proteins into new virions within the host cell.

Release

Exit of new virions from the host cell by budding, apoptosis, or exocytosis (viral shedding).

Lytic Cycle

Active phage cycle in which viral genomes are replicated, new phages assembled, and the host cell lysed.

Lysogenic Cycle

Passive phage cycle in which the phage genome integrates into the host genome and replicates with it until induced to enter the lytic phase.

Restriction Enzymes

Bacterial enzymes that cut foreign phage DNA at specific sequences as a defense mechanism.

CRISPR-Cas System

Bacterial adaptive immune system that recognizes and cleaves invading viral genomes; repurposed for genome editing.

Prion

Infectious, misfolded protein that induces misfolding of normal proteins, leading to disease.

Viroid

Small, circular single-stranded RNA molecule that infects plants without coding for proteins.

Endocytosis (viral)

Host cell process that engulfs non-enveloped viruses or enveloped viruses lacking fusion entry.

Budding

Mechanism by which enveloped viruses acquire their membrane and exit the host cell without immediate lysis.

Apoptosis (in viral release)

Programmed cell death sometimes triggered by viruses to facilitate release of progeny virions.

Host Surface Mutation

Changes in bacterial surface proteins that prevent phage recognition and attachment.