Micro F Comprehensive Study Guide on Viruses, Viroids, and Prions

Vocabulary practice flashcards covering structural features, replication cycles, and medical significance of viruses, viroids, and prions based on lecture material.

Viruses

Acellular infectious agents containing either a DNA or RNA genome, surrounded by a protein coat, that lack cellular membranes, cytosol, and organelles, and cannot carry out metabolic functions or reproduce independently.

Virion

The extracellular state of a virus that consists of a nucleic acid core encased within a protein capsid, sometimes surrounded by an outer phospholipid envelope.

Capsid

The protein coat that surrounds and protects the nucleic acid genome of a virus.

Capsomeres

The repeating protein subunits that assemble to make up the viral capsid.

Viral envelope

An outer phospholipid bilayer and protein layer surrounding the capsid of certain viruses, derived from the host cell membrane during viral exit.

Spikes

Virally encoded glycoproteins located on the outer surface of an enveloped virus that mediate binding to host cell receptors.

Generalists

Viruses capable of infecting many kinds of cells or multiple different host species, such as SARS-CoV-2 targeting the ACE2 receptor across various cell types and mammals.

Bacteriophage

A virus that specifically infects and replicates within bacterial host cells.

Lytic replication cycle

A viral replication pathway consisting of five stages (attachment, entry, synthesis, assembly, and release) that culminates in the lysis and death of the host cell.

Lysogeny

A modified viral replication cycle in bacteriophages where the viral genome integrates into the bacterial chromosome instead of immediately destroying the host cell, replicating alongside the host until induced.

Lysogenic conversion

A phenomenon that occurs when an integrated temperate phage introduces a viral gene that alters the phenotype of the host bacterium.

Induction

The event during lysogeny in which environmental signals trigger the integrated viral genome to excise from the bacterial chromosome and re-enter the lytic cycle.

Direct penetration

An entry mechanism in nonenveloped animal viruses where capsid proteins bind host receptors and inject the viral genome directly into the host cytoplasm while the capsid remains outside.

Membrane fusion

An entry mechanism used by enveloped animal viruses where the viral envelope fuses directly with the host cell cytoplasmic membrane, releasing the nucleocapsid into the host cell interior.

Uncoating

The intracellular removal of the viral capsid following entry, which exposes the viral nucleic acid genome inside the host cell.

Positive-sense single-stranded RNA (+ssRNA)

Viral RNA that can be directly recognized and translated into viral proteins by host cell ribosomes immediately upon entering the cell, functioning like mRNA.

Negative-sense single-stranded RNA (-ssRNA)

Viral RNA that cannot be directly translated by host ribosomes as mRNA and must first be transcribed into complementary positive-sense mRNA.

Retroviruses

A category of single-stranded positive-sense RNA viruses, such as HIV, that utilize the enzyme reverse transcriptase to synthesize a double-stranded DNA intermediate from their RNA genome.

Budding

An extrusion process through which enveloped virions acquire their outer membrane from a host cell without immediately rupturing or killing the host cell.

Persistent infection

An infection in which virions are released continuously and slowly through budding, allowing host cells to remain alive and shed virus over extended periods.

Latency

A condition in which animal viruses remain dormant within host cells for years without active viral replication, permanently integrating their genome as proviruses into host DNA.

Neoplasia

The uncontrolled cell division occurring in a multicellular animal, which results in the development of a mass of cells known as a tumor.

Metastasis

The process by which malignant cancer cells spread from their initial site of origin to colonize and produce tumors in other regions of the body.

Proto-oncogenes

Normal cellular genes that promote cell division and cellular growth when functioning under strict biological regulation.

Oncogenes

Hyperactivated or mutated forms of proto-oncogenes that stimulate excessive, unregulated cell division and can lead to cancer.

Tumor suppressor genes

Normal cellular regulatory genes that function to inhibit or shut down cell division, whose inactivation removes essential checkpoints and promotes tumor development.

Viroids

Small, infectious, circular single-stranded RNA molecules that completely lack a capsid, do not code for proteins, and cause disease exclusively in plants.

Prions

Infectious proteinaceous agents that contain no nucleic acid and induce neurodegenerative disease by causing normal brain proteins to misfold.

Cellular PrP

The normal, non-pathogenic mammalian membrane protein characterized predominantly by an alpha-helical secondary structure.

Prion PrP

The disease-causing, misfolded conformational variant of the cellular PrP protein, characterized by beta-pleated sheets, which causes spongiform encephalopathy and large vacuoles in brain tissue.