Microbiology chapter 13

Viruses and stuff

What does “obligate intracellular parasite” mean?

Viruses cannot live or reproduce on their own; they must enter a living host cell.

Why do viruses require living host cells to multiply?

They lack the machinery (ribosomes, enzymes, ATP production) needed for reproduction.

What type of genetic material do viruses have?

Either DNA or RNA — never both.

What is a capsid?

The protein coat surrounding viral genetic material; made of capsomeres.

What are spikes?

Protein projections used for attachment; may cause hemagglutination.

Do viruses have ribosomes or ATP production?

No, they must use the host’s ribosomes and ATP.

What is a virus’s host range?

The spectrum of host cells a virus can infect.

What determines host range?

Specific attachment sites (receptors) on the host cell.

What is a virion?

A fully developed, infectious virus particle.

What forms can viral genomes take?

ssDNA, dsDNA, ssRNA, dsRNA; linear, circular, or segmented.

What does genome size influence?

How many proteins a virus can make and its complexity.

What are the 4 main virus shapes?

Helical, Polyhedral, Enveloped, Complex.

Example of helical viruses?

Rabies, Ebola.

Example of polyhedral viruses?

Adenovirus, poliovirus.

Example of complex viruses?

Bacteriophages.

What does the Baltimore system classify?

Viruses based on nucleic acid type and method of mRNA production.

Virus family names end in what suffix?

-viridae

Virus genus names end in what suffix?

-virus

How are bacteriophages grown in the lab?

In bacteria on agar plates → plaques form.

What is a plaque?

A clear zone where the virus has killed bacteria.

3 ways to grow animal viruses?

Living animals, embryonated eggs, cell cultures.

What are cytopathic effects (CPE)?

Visible damage in infected host cells.

What does ELISA detect?

Viral antigens using antibodies.

What technique detects viral nucleic acids?

Polymerase Chain Reaction (PCR) is used to amplify and detect viral nucleic acids in samples.

What two things must viruses do to replicate?

Invade a host cell; use host metabolic machinery.

What are the general stages of viral replication?

Attachment → Entry → Uncoating → Biosynthesis → Maturation → Release.

What are the two phage cycles?

Lytic and lysogenic.

What is lysogeny?

Phage DNA integrates into host DNA (prophage).

What is specialized transduction?

Phage transfers specific bacterial genes.

What are the two viral entry methods?

Receptor-mediated endocytosis & fusion.

How do enveloped viruses exit the host cell?

Budding.

How do non-enveloped viruses exit?

Cell rupture.

Where do most DNA viruses replicate?

In the nucleus.

What enzyme do RNA viruses use for replication?

RNA-dependent RNA polymerase.

What is positive-sense RNA (+)?

Acts directly as mRNA.

What is negative-sense RNA (−)?

Must be converted to +RNA first.

What does reverse transcriptase do?

Converts viral RNA into DNA.

What is a provirus?

Viral DNA integrated into host genome.

What is an oncogene?

A mutated proto-oncogene that causes uncontrolled cell growth.

Can viral cancers be transmitted person-to-person?

No.

Examples of DNA oncogenic viruses?

HPV, Hepatitis B, Epstein-Barr virus.

What RNA viruses can cause cancer?

HTLV-1, HTLV-2.

What is a latent infection?

Virus remains inactive but can reactivate (e.g., herpes).

What is a persistent infection?

Slow, chronic viral infection (e.g., SSPE)

How do plant viruses enter cells?

Through wounds or insect vectors.

What are viroids?

Naked RNA molecules that infect plants.

What are virusoids?

Viroids enclosed in protein; require a helper virus.

What are prions made of?

Protein only (no DNA/RNA).

How do prions cause disease?

Misfolded prions convert normal proteins → accumulate → brain damage.

Examples of prion diseases?

Mad cow, CJD, fatal familial insomnia, scrapie.