Chapter 13- Viruses, Viroids, and Prions

virus

infectious agent consisting of DNA or RNA surrounded by a protein coat (capsid); in some cases enveloped by a host-derived membrane

capsid

protein coat surrounding the nucleic acid in a virus

nucleocapsid

protein coat and nucleic acid together

lytic infection

an infection where the infectious agent immediately replicates & destroys host cells

latent infection

an infection where the infectious agents is present but not active

lysogenic infection

an infection with a temperate (latent) phage that results in a quiescent virus residing in the host genome where it replicates along with the host chromosome. upon some future signal, latent virus awakens and becomes lytic

spikes

involved in host recognition; always outside of the virion

icosahedral

geometric shape of viruses with 20 sides

helical

virus shaped like a hollow tube or cylinder

what are the two most common virus morphologies?

icosahedral and helical

what is the third less common shape of viruses?

complex

how many bacteriophages exist on earth?

10 raised to 31; most numerous of all biological entities

matrix protein

structural proteins linking the envelope to the virus core

viruses are either naked or ______?

enveloped

bacteriophage

viruses that infect bacteria

sheath

contractile structure that surrounds tail on a bacteriophage to facilitate delivery of genetic material into host cell

baltimore classification

classification of 7 categories of viruses based on the type of nucleic acid

+ssRNA viruses

RNA can be transcribed directly

-ssRNA viruses

RNA must be converted to the + strand or to dsRNA before being transcribed

International Committee on Taxonomy of Viruses (ICTV)

committtee charged with developing a universal taxonomic scheme to name and classify viruses

what is the ICTV classification based on?

physical and chemical properties

A T4 bacteriophage can make how many copies of itself in how many minutes?

200, 30

what must be separated from the capsid before a virus can replicate?

nucleic acid

temperate phage

can be lytic, or become lysogenic shortly after infection

lysogenic conversion

when infecting bacteria produce toxins because they have their own bacteriophage infections that supplies the viral RNA polymerase to produce the disease state

what part of the virus recognizes the receptor on the cell/tissue it infects?

spikes

examples of diseases displaying lysogenic conversion

cholera, diptheria, scarlet fever

what type of viral infection might allow a bacterium to pass a virus to its daughter cells?

lysogenic

budding

process where chronically infected viruses release coated virus

what is an example of a lytic infection?

rhinovirus (common cold)

what is an example of a temperate phage?

lambda

plaque assay

method to measure infectious viruses in a sample based on formation of plaques

prophage

genetic material of a bacteriophage, incorporated into the genome of a bacterium and able to produce phages if specifically activated

what is an example of a lytic virus?

rhinovirus (common cold)

what is an example of a lysogenic virus?

herpes simplex 1

what is a plaque?

a hole that demonstrates lysis caused by a virus

how do bacteriophages infect?

by injecting their genetic material into host bacterium

how do we detect viruses?

with the transmission electron microscope invented in 1931