Introduction to Virology – Viruses, Structure, Classification & Infection

A comprehensive set of vocabulary flashcards summarizing the key terms and concepts from the lecture on viral structure, classification, genetics, replication and infection pathways.

Virus

A minute, non-cellular infectious particle consisting of nucleic acid enclosed in a protein coat (and sometimes a lipid envelope) that can replicate only inside a living host cell.

Virology

The scientific study of viruses and viral diseases.

Virion

A complete, infectious viral particle existing outside a host; typically 10–100 times smaller than a bacterial cell.

Capsid

The protective protein coat that surrounds a viral genome.

Capsomere

An individual protein subunit that builds up the viral capsid.

Nucleocapsid

The viral genome together with its associated nucleoproteins, enclosed by the capsid.

Viral envelope

A lipid bilayer, derived from the host membrane, that surrounds the capsid of some viruses and bears viral glycoproteins.

Viral glycoprotein

Envelope-embedded protein (often with attached carbohydrates) that mediates virus attachment and entry into host cells.

Enveloped virus

A virus whose nucleocapsid is surrounded by a lipid envelope; generally more sensitive to heat, pH and disinfectants.

Non-enveloped (naked) virus

A virus lacking a lipid envelope; typically more resistant to environmental stresses.

Helical symmetry

Capsid architecture in which protein subunits form a spiral or rod-shaped structure around the genome (e.g., Paramyxovirus).

Icosahedral symmetry

Roughly spherical capsid built from 20 triangular faces (e.g., Reovirus, Picornavirus).

Complex virus

Virus with intricate structure that is neither purely helical nor icosahedral (e.g., Poxvirus, bacteriophage T4).

Bacteriophage

A virus that infects bacteria; often has head-and-tail morphology.

Genome (viral)

The total genetic content of a virus, composed of either DNA or RNA but never both.

DNA virus

A virus whose genome is DNA; directs host replication machinery to synthesize viral DNA and proteins.

RNA virus

A virus whose genome is RNA; encodes its own RNA-dependent enzymes for replication.

Single-stranded DNA (ssDNA) virus

DNA virus with a single-stranded genome (e.g., Parvovirus).

Double-stranded DNA (dsDNA) virus

DNA virus with a double-stranded genome (e.g., Herpesvirus, Adenovirus).

Single-stranded RNA (ssRNA) virus

RNA virus possessing a single-stranded genome; subdivided into positive-sense and negative-sense types.

Positive-sense RNA (+RNA) virus

ssRNA virus whose genome can serve directly as mRNA (e.g., Picornavirus, Flavivirus).

Negative-sense RNA (–RNA) virus

ssRNA virus whose genome is the complement of mRNA and must be transcribed before translation (e.g., Orthomyxovirus).

Double-stranded RNA (dsRNA) virus

RNA virus with a double-stranded genome (e.g., Reovirus).

Retrovirus

Enveloped ssRNA virus that uses reverse transcriptase to synthesize a DNA copy for integration into the host genome (e.g., HIV).

Reverse transcriptase

Retroviral enzyme that copies RNA into complementary DNA (cDNA).

Baltimore classification

Virus grouping system based on the pathway used to generate viral mRNA (seven classes, I–VII).

Host range

The spectrum of host species or cell types a virus can infect (animal, plant, bacterium, insect).

Animal virus

Virus that infects animal (including human) cells, e.g., Influenza virus, Rabies virus.

Plant virus

Virus that infects plants; replication is obligate within plant cells (e.g., Tobacco mosaic virus).

Insect virus

Virus that infects insects; some serve as biocontrol agents (e.g., Ascovirus).

Lytic infection

Viral replication cycle that culminates in host cell lysis and release of viral progeny.

Attachment (adsorption)

Initial step of infection where a virion binds to specific receptors on the host cell surface.

Penetration

Entry of the viral nucleic acid (and sometimes capsid) into the host cell.

Uncoating

Process by which the viral genome is freed from the capsid/envelope inside the host cell.

Replication (viral)

Synthesis of viral genomes and proteins using host and viral enzymes.

Assembly

Self-organization of newly made viral genomes and proteins into complete virions.

Release

Exit of mature virions from the host cell by lysis, budding, or cell death.

Respiratory (airborne) entry

Inhalation route through which viruses like influenza and measles gain access via the respiratory tract.

Faecal-oral entry

Ingestion route; viruses such as Hepatitis A and Rotavirus enter via contaminated food or water.

Urogenital transmission

Sexual route for viruses like HIV, human papillomavirus and herpes simplex.

Conjunctival transmission

Viral entry through the eye surface, possible with adenoviruses or herpes simplex.

Skin inoculation

Virus introduction through breaks, punctures, or arthropod bites (e.g., Rabies virus, Dengue virus).