Introductory Microbiology - Acellular Pathogens (Vocabulary Flashcards)

Vocabulary flashcards covering key concepts from acellular pathogens and viral biology: structure, taxonomy, replication cycles, transmission, and special cases (bacteriophages, retroviruses, prions, viroids, and coronavirus-like concepts as per notes).

Virus

Acellular infectious agent with a genome (DNA or RNA) and a protein coat (capsid); some have a phospholipid envelope; incapable of metabolism or independent growth; obligate intracellular parasite with extracellular virion and intracellular forms.

Capsid

Protein coat that encloses the viral genome; built from subunits called capsomeres.

Capsomere

Individual protein subunit that assembles to form the capsid.

Envelope

Phospholipid bilayer acquired from the host cell membrane surrounding some viruses; contains viral spikes.

Naked (non-enveloped) virus

Virus lacking a lipid envelope; generally more resistant to environmental factors and often causes host lysis on exit.

Spikes

Viral glycoproteins extending from the capsid or envelope that mediate attachment to host receptors.

Hemagglutination (H) & Neuraminidase (N)

Influenza virus surface spikes used to classify strains (e.g., H1N1); involved in attachment and release.

Tissue tropism

Host and cell specificity; viruses infect particular cell types or tissues.

ICTV

International Committee on Taxonomy of Viruses; classifies viruses into families and genera based on genetics, chemistry, morphology, and replication; uses family viridae and genus virus; no binomial nomenclature.

Bacteriophage

Virus that infects bacteria; genome in a polyhedral head; tail sheath, fibers, and pins for attachment and injection of DNA.

Lytic cycle

Virulent phage lifecycle ending in host cell lysis and production of new virions.

Lysogenic cycle

Temperate phage lifecycle where phage DNA integrates as a prophage into the bacterial chromosome and is replicated with the host.

Prophage

Integrated, inactive phage genome within the bacterial chromosome.

Lysogen

Bacterial host carrying a prophage.

Lysogenic conversion

Change in host phenotype due to prophage-encoded genes, often including toxins or virulence factors.

Prophage induction

Process by which the prophage is excised and the phage enters the lytic cycle.

Transduction

Horizontal gene transfer between bacteria mediated by bacteriophages.

Generalized transduction

Transduction by virulent phages in the lytic cycle, transferring random pieces of bacterial DNA.

Specialized transduction

Transduction by temperate phages after induction, packaging nearby bacterial genes with prophage DNA.

Retrovirus

RNA virus that uses reverse transcriptase to convert RNA into DNA, which integrates into the host genome as a provirus.

Reverse transcriptase

Enzyme that converts viral RNA into DNA in retroviruses.

Provirus

Integrated viral DNA within the host genome after reverse transcription.

HIV

A retrovirus that uses gp120 to bind CD4 with coreceptors (CCR5/CXCR4); reverse transcribes RNA, integrates as provirus, and matures via protease.

Entry mechanisms

Attachment to receptors followed by entry via direct penetration, membrane fusion, or endocytosis.

Budding

Exit of enveloped viruses from a host cell through budding from membranes, often leading to chronic infection.

Prions

Proteinaceous infectious particles with no DNA or RNA; PrPc misfolds to PrPSc, causing transmissible spongiform encephalopathies and rapid neurodegeneration.

Viroids

Small naked ssRNA plant pathogens with no protein coat and no encoding of proteins.

Virusoids

Non-self-replicating ssRNA molecules that require helper viruses (e.g., Hepatitis D requires Hepatitis B) to infect.

Chronic infections

Infections where the virus persists with long-term or recurrent symptoms; virus detectable for extended periods (e.g., HIV, Hepatitis, Herpes).

Latent infections

Initial acute infection followed by dormancy; virus remains in tissues (e.g., Varicella-zoster) and can reactivate later as shingles.