Ch. 7 Viruses and Prions

Viruses can be described as ___ or ___.

active; inactive

largest viruses

Pandoravirus; 1 micrometer

Mimivirus; 450 micrometers

smallest viruses

Parvoviruses .02 micrometers

Yellow fever virus 22 micrometers

capsid

shell surrounding viral nucleic acid

nucleocapsid

capsid and nucleic acid together

envelope

a modified piece of the host membrane; not found in all viruses

spikes

project from either the nucleocapsid or envelope; allow viruses to dock with their host cells

virion

fully formed virus able to establish infection in a host

capsomeres

identical protein subunits that spontaneously self assemble to form the capsid

helical capsid

rod-shaped capsomeres that form a continuous helix around the nucleic acid

icosahedral capsid

three-dimensional, 20 sided figure with 12 evenly spaced corners

complex capsids

. found in bacteriophage and rabies

. have multiple types of proteins

. take shaped that are not symmetrical

positive-sense RNA

single-stranded RNA genomes ready for immediate translation into proteins

negative -sense RNA

RNA genomes that need to be converted into the proper form to be made into proteins

polymerases

synthesize DNA and RNA

replicases

copy RNA

reverse transcriptase

synthesizes DNA from RNA

arenaviruses

pack along host ribosomes

retroviruses

“borrow” the host’s tRNA molecules

viral orders

suffix -virales

viral families

suffix -viridae

virus genera

suffix -virus

adsorption/attachment

virus encounters a susceptible host and adsorbs specifically to receptor sites on the cell membrane

host range

a virus can invade its host cell only through compatible host molecules

penetration

endocytosis: entire virus is engulfed the the cell and enclosed in a vacuole or vesicle

uncoating

enzymes in the vacuole dissolve the envelope and capsid, releasing the virus into the cytoplasm

synthesis

. viral nucleic acid takes control over the host’s synthetic and metabolic machinery

. Mechanism depends on whether the virus is a DNA or RNA virus

. RNA viruses replicate in the cytoplasm and DNA viruses replicate in the nucleus

release

. enveloped viruses are released by budding or exocytosis

cytopathic effects

virus-induced damage to the cell at alters its microscopic appearance

inclusion bodies

compacted masses of viruses or damaged cell organelles in the nucleus or cytoplasm

syncytia

fusion of multiple host cells into single large cells containing multiple nuclei

provirus

viral DNA incorporated into the DNA of the host

chronic latency state

periodic reactivation after a period of viral inactivity

oncogenic viruses

viruses that cause cancer; experts estimate that up to 13% of human cancers are caused by viruses

transformation

Virus carries genes that directly cause cancer; Virus produces proteins that induce a loss of growth regulation in the cell

bacteriophage

virus that infects bacteria; lytic and lysogenic cycles

lytic phase/ cycle

life cycle of a bacteriophage that ends in the destruction of the bacterial cell

lysogenic cycle

bacteriophage becomes incorporated into the host cell DNA

prophage: an inactive state in which phage DNA is inserted into the host chromosome

induction: activation of a prophage in a lysogenic cell to progress directly into viral replication and the lytic cycle

lysogenic conversion

the acquisition of a new trait from a temperate phage; responsible for the diphtheria toxin, cholera toxin, and botulism toxin

primary purposes of viral cultivation

1. isolate and identify viruses in clinical specimens

2. prepare viruses for vaccines

3. do detailed research on viral structure, multiplication cycles, genetics, and effects on host cells

benefits of using bird embryos for viral cultivation

. Embryonic development occurs in a protective shell
• Intact and self-supporting unit with its own sterile environment and nourishment
• Furnishes several embryonic tissues that support viral multiplication

continuous cell cultures

• Have altered chromosome numbers
• Grow rapidly
• Show changes in morphology
• Can be continuously subcultured if they are given fresh nutrient media

plaques

clear, well defied patches in the cell sheet that develops when viruses released from an infected cell radiate out to surround cells and infect them