Comprehensive Virus Structure, Lifecycle, and Classification for Biology Students

How do viruses compare to other microorganisms?

Viruses are nonliving particles needing a host to reproduce, contain only DNA or RNA, lack metabolism and organelles, and are smaller. Microorganisms like bacteria, fungi, and protozoa are living cells, can reproduce on their own, and have metabolism and ribosomes/organelles.

What is the function of viral capsids?

Protect the nucleic acid, help virus attach to host cells, and give the virus shape.

What is the structure of a viral capsid?

Protein shell made of capsomeres; can be helical, icosahedral, or complex.

What is the difference between enveloped and naked viruses?

Enveloped viruses have a lipid membrane and are sensitive to heat/detergents; naked viruses lack an envelope and are more resistant.

What is the role of viral spikes (surface proteins)?

Spikes allow attachment to host receptors, determine host range, help entry/exit, and are targets for immune response.

What nucleic acid configurations can viruses have?

DNA or RNA; double- or single-stranded; linear or circular; segmented or non-segmented.

What is a prophage?

Bacteriophage DNA inserted into the bacterial chromosome during lysogeny.

What is the difference between virions and viroids?

Virions are complete virus particles containing nucleic acid + capsid ± envelope. Viroids are naked infectious RNA with no capsid and infect plants only.

How are virus family names written?

End in -viridae (ex: Herpesviridae).

How are virus genus names written?

End in -virus (ex: Herpesvirus).

What are the 5 steps in the life cycle of animal viruses?

1. Adsorption - virus attaches to host. 2. Penetration - enters by fusion or endocytosis. 3. Uncoating - capsid breaks down; genome released. 4. Synthesis - viral RNA/DNA and proteins produced. 5. Assembly & Release - new virions form and exit by budding or lysis.

What are cytopathic effects (CPEs)?

Structural changes in host cells caused by viruses.

Give 3 examples of cytopathic effects.

Cell lysis, syncytia formation, inclusion bodies, cell rounding.

What is an oncogenic virus?

Virus that causes cancer by altering host DNA.

Give 3 examples of oncogenic viruses.

HPV, Epstein-Barr virus, Hepatitis B/C viruses.

What is the difference between lysogenic and lytic bacteriophage infections?

Lytic: virus replicates immediately and lyses (kills) host cell. Lysogenic: viral DNA integrates as a prophage and stays dormant until activated.

What are the steps in bacteriophage multiplication?

Adsorption → Penetration → Synthesis → Assembly → Release (lysis).

What are three purposes of cultivating viruses?

Study virus biology, produce vaccines, diagnose infections/test treatments.

What are three methods for cultivating viruses?

Live animals, embryonated eggs, cell/tissue cultures.

Why are viruses important in human disease?

Cause many acute/chronic diseases, cancers, immune disorders, and impact global health.

What are prions?

Infectious misfolded proteins with no nucleic acid.

How do prions differ from viruses?

Prions have no DNA/RNA, no capsid, and cause neurodegenerative diseases.

Why are antiviral drugs difficult to design?

Viruses use host cell machinery, so drugs risk harming host cells.

What is a plaque assay?

Test measuring viruses by counting clear zones (plaques) where viruses killed bacteria.

What limits virus host range?

Specific binding between viral spikes and host cell receptors.

What is the difference between acute and persistent viral infections?

Acute: fast, short, virus cleared quickly (flu). Persistent: long-lasting, slow release, can remain for life (HIV, hepatitis B).

What type of virus is adenovirus?

Non-enveloped, icosahedral, dsDNA; causes colds and conjunctivitis.

What type of virus is myxovirus (orthomyxovirus)?

Enveloped, helical, segmented RNA; causes influenza.

What type of virus is herpesvirus?

Enveloped, dsDNA; causes cold sores, genital herpes, chickenpox/shingles.

What type of virus is rhinovirus?

Naked, icosahedral, ssRNA; causes common cold.

What type of virus is rhabdovirus?

Bullet-shaped, enveloped, ssRNA; causes rabies.

What type of virus is filovirus?

Filamentous, enveloped, ssRNA; causes Ebola and Marburg.

What type of virus is parvovirus?

Smallest DNA virus, ssDNA, naked; causes Fifth disease ("slapped cheek").

What type of virus is papillomavirus?

Naked, dsDNA; causes warts and HPV cancers.

What type of virus is influenza virus?

Enveloped, segmented ssRNA; causes seasonal flu.