Viruses - Bio Exam 2

What is a virus?

An acellular obligate parasite lacking key characteristics of life.

Filterable infectious agents

Historical term for viruses because they pass through porcelain bacteria filters.

Viral size range

Most measure 20 to 250 nm, requiring electron microscopy.

Reduction hypothesis

Viruses evolved from cellular organisms becoming increasingly dependent on hosts.

Escape hypothesis

Viruses evolved from genetic material that escaped from cells.

Virus-first hypothesis

Viruses evolved from self-replicating molecules prior to cellular evolution.

Virion

A single, inert virus particle containing a nucleic acid genome.

Capsid

A protein shell enclosing the viral genome, made of capsomeres.

Helical capsids

Capsomeres arranged in a spiral around the viral genome.

Icosahedral capsids

Symmetrical structures with 20 triangular faces.

Viral envelopes

Phospholipid membranes derived from host cells surrounding the capsid.

Viral spike proteins

Glycoproteins that facilitate attachment to specific host-cell surface receptors.

Viral mutation rates

Generally very high, especially among RNA viruses due to error-prone replication.

Lytic cycle

Active viral replication leading to immediate host cell lysis.

Lysogenic cycle

Latent viral infection where DNA integrates as a prophage.

Positive-sense RNA (+RNA)

Viral RNA that can function directly as mRNA in host cells.

Negative-sense RNA (-RNA)

Viral RNA complementary to mRNA, requiring viral RdRp to copy.

RNA-dependent RNA polymerase (RdRp)

Error-prone viral enzyme that copies RNA into RNA.

Retroviruses

Viruses using reverse transcriptase to produce DNA from a +ssRNA genome.

Baltimore system

Classifies viruses into seven groups based on genome type and mRNA production.

Viral tropism

The specific cells and tissues a virus is capable of infecting.

Five stages of viral infection

Attachment, entry, replication/protein synthesis, assembly, and egress.

Viral egress methods

Cell lysis, budding, and exocytosis.

Acute infection

Rapid viral replication followed by immune clearance.

Latent infection

Viral genome persists with little virus production, capable of reactivation.

Oncogenic viruses

Viruses that contribute to cancer development by disrupting cell cycle control.

Live attenuated vaccines

Contain weakened, replication-competent viruses providing strong, long-lasting immunity.

Inactivated vaccines

Whole viruses rendered noninfectious through chemical or physical treatment.

Subunit vaccines

Contain specific viral antigens or surface proteins produced via recombinant technology.

Nucleic acid vaccines

Deliver genetic instructions for producing a viral antigen to stimulate immunity.

Antiviral drug targets

Specific viral processes like entry, replication, integration, and egress.