Viruses, Viroids, and Prions Lecture 12

Bacteriophages

viruses that infect bacteria

what is the host range

the spectrum of host cells a virus can infect

Where can bacteriophages attach on bacteria?

Cell wall, fimbriae or flagella

where do animal viruses typically bind on host cells

cell wall, fimbriae or flagella

What shapes can viral nucleic acid have?

Linear, circular, or segmented.

What is the size range of viral genomes?

A few thousand to about 250,000 nucleotides.

what is a virion

a complete fully developed viral particle

what types of nucleic acid can viruses contain

DNA or RNA

What is a capsid?

The protein coat of a virus made of capsomere subunits.

What is a viral envelope?

A lipid-protein-carbohydrate coating external to the capsid, derived partly from the host cell membrane.

What are viral spikes?

Carbohydrate-protein projections on some enveloped viruses used for attachment.

What is a helical virus? Give examples.

Virus with a hollow cylindrical helical capsid; examples: rabies, Ebola.

What is a polyhedral virus? Give examples.

Many-sided (often icosahedral) capsid; examples: adenovirus, poliovirus.

What is the general shape of most enveloped viruses?

Roughly spherical.

What is a complex virus? Give an example.

Virus with complicated structure; example: bacteriophage.

What is the function of the bacteriophage head?

Holds and protects nucleic acid.

What is the role of the phage tail and sheath?

Tail delivers nucleic acid; sheath contracts to inject it into the host.

What do phage fibers and baseplate do?

Recognize binding sites and anchor the virus to the host cell wall.

What happens in the lytic cycle?

Phage replicates and lyses (kills) the host cell.

What happens in the lysogenic cycle?

Phage DNA integrates into host DNA and replicates with it.

What is phage conversion?

Host cell gains new traits from integrated phage DNA.

What is specialized transduction?

Transfer of specific host genes by lysogenic phages.

What are the steps of animal virus replication?

Attachment → entry → uncoating → biosynthesis → maturation → release.

How are enveloped vs nonenveloped viruses released?

Enveloped: budding; nonenveloped: cell rupture.

What is the Baltimore classification system based on?

Viral nucleic acid type and how mRNA is produced.

What suffixes indicate viral taxonomy ranks?

Order: -ales; Family: -viridae; Genus: -virus.

What defines a viral species?

Viruses sharing the same genetic information and host niche.

How do plant viruses enter plant cells?

Through wounds or insect damage.

What are viroids?

Short pieces of naked RNA that infect plants.

What are prions?

Proteinaceous infectious particles with no nucleic acid.

How can prion diseases be transmitted?

Ingestion, transplant, or contaminated instruments; also inherited.

Name examples of prion diseases.

Mad cow disease, Creutzfeldt-Jakob disease, scrapie, fatal familial insomnia.