Glossary of Microbiology: Chapter 16

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What are the five traits of viruses?
The five traits of viruses are: 1) acellullar (lack true membrane), 2) DNA or RNA - Not both, 3) obligate intracellular parasites, 4) self-assemble - no fission, and 5) nucleic acid & protein coat
Define virion
A virion is a complete virus particle consisting of one ore more molecules of DNA or RNA enclosed in a protein coat.
Define nucleocapsid
A nucleocapsid consists of the nucleic acid and its protein coat/capsid.
Define capsid
A capsid is the protein coat that surrounds a virion's nucleic acid.
Define envelope
The envelope is an outer membranous layer that surrounds the nucleocapsid in some viruses.
How big are viruses?
Viruses range in size, with the largest around 400nm and the smallest at 10nm in diameter.
How are viruses grown?
Viruses are replicated using a host cells machinery. The virion injects its DNA or RNA into a host cell, cleaves the host's DNA, then uses the hosts machinery and nucleotides to synthesize its own DNA. To grow viruses, virologists must inject viruses into the proper host: bacteriophage - bacteria, plant viruses - plants, animal viruses - animals, embryonated chicken eggs, or cell culture monolayers.
What are pocks?
Pocks are local tissue lesions found in infected embyonated chicken eggs as a result of the virus.
What are plaques?
Plaques are clear areas in a lawn of bacteria or a localized area of cell destruction in a layer of animal cells that results from the lysis of the bacteria by bacteriophages or the destruction of the animal cells by animal viruses.
What are cpe's?
Cpe's or cytopathic effects are observable changes that occur in cells as a result of viral replication. Examples include ballooning, binding together, clustering, or even death of the cultured cells.
How can you assay for viruses?
You can assay for viruses by direct EM count, counting directly with the electron microscope and using latex beads as an internal standard, hemaglutination assay, based on the binding of viruses to red blood cells, plaque assays, in which plaques are counted to establish a count of pfu's (the two are not equal but proportional), or by the end point method in which orgs or a cell culture are incoluated with serial dilutions of a virus suspension and the results of the end point dilution are used to find the LD50 or ID50.
What are LD50 and ID50?
LD50, or lethal dose 50, refers to the dose or number of organisms that will kill 50% of an experimental group of hosts within a specified time period. ID50, or infection dose 50, refers tl the dose or number of organisms that will infect 50% of an experimental group of hosts within a specified time.
What is the genome of a virus?
The genome that enters a virus is terminally redundant, it has direct repeats at the ends. During replication concatemers are formed. 102% of the genome is packaged into each 'head' during assembly. Genomes that leave are circularly permuted.
Are animal, plant, and bacterial viruses usually DNA or RNA?...single-stranded or double-stranded?
Animal: ssDNA, dsDNA, ssRNA, dsRNA; Plant: usually ssRNA; and Bacteriophage: usually dsDNA, but can be ssDNA and ssRNA
What are mono- and multipartite (segmented) genomes?
Monopartite means that all of the genome is in one piece, while multipartite or segmented means that different information is on different pieces of the genome.
What is meant by postive and negative strands?
A positive strand means that the genome acts as mRNA, (may be capped and poly-adenylated) while a negative strand means that the genome acts as the template for mRNA.
What are three general classes of capsid morphologies?
Three general classes of capsid morphology are: 1) helical, 2) icosahedral (20 equilateral triangular sides), and 3) Complex (a. combined (binal symmetry) and b. irregular (doesn't fit other patterns).
What is binal symmetry?
Binal symmetry is the symmetry of some virus capsids (eg. those of comple phages) that is a combination of icosahedral and helical symmetry.
What are capsomers and protomers?
Capsomers are capsid proteins - the ring-shaped morphological unit of which icosahedral capsids are consturcted. Protomers are the individual subunits that make up capsomers.
Where are pentamers and hexamers found?
Pentamers are capsomers with 5 protomers that are usually only found at vertices and associate with 5 other capsomers. Hexamers are capsomers with 6 protomers that are found on faces and edges and associate with 6 other capsomers.
What are envelopes?
Envelopes are outer membranous layers surrounding the nuclecapsid.
Which types of viruses are most likely to have envelopes?
Mostly animal viruses are the type likely to have envelopes.
What is the derivation of the envelope and its components?
Animal virus envelopes usually arise from host cell nuclear or plasma membranes; their lipids and carbohydrates are normal host constituents. Envelope proteins are coded for by the virus genes.
What are peplomers?
Peplomers or spikes are proteins or protein complexes that extend from the virus envelope and often are important in virion attachment to the host cell surface.
What do peplomers do?
Peplomers help attach the virion to the host cell surface.
What parameters are used in the taxonomic classification of viruses?
The parameters used in the taxonomic classification of viruses are: Host preference, Nucleic acid type, Nucleic acid strandedness, Envelope presence, Capsid symmetry, size, and other characteristics.

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