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Chapter 5 (NOTES)
TEST TWO
38
Biology
Undergraduate 4
10/14/2013

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Term
Virus
Definition
Obligate inracellular parasites
Require host cells to reproduce
10-100 nm
Term
Walter Reed
Definition
Yellow fever (human disease) was caused by a virus transmitted by mosquitos
Term
Bacteriophage
Definition
Virus that only attacks bacteria
Term
Retrovirus
Definition
Reverse mechanism to change RNA to DNA to put it into your cells
Term
Structure of Virus
Definition
Single or double or partially stranded DNA or RNA
Capsid and sometimes envelope
Term
Capsid
Definition
Protein shell composed of many capsomere proteins
Surrounds the genome
Helical or icosahedral symmetry
Term
Nucleocapsid
Definition
Capsid and the genome together
Term
Envelope
Definition
Plasma membrane around the capsid
Virus is "naked" if it doesn't have one
Term
Replication Cycle
Definition
Adhere, penetrate, uncoat, early synthesis, late synthesis, assembly, and exit.
Term
Most important part in the viral replication cycle
Definition
Entry: in animal cells, they don't have to contend with a cell wall. In other cells, they do.
Term
Animal Viruses
Definition
Many are enveloped. Not all infections end in cell lysis or cell death.
Term
Why are animal viruses enveloped?
Definition
The envelope allws it to get into the host cytoplasmic membrane.
Term
What results do some animal viruses have on cells? (not including lysis)
Definition
Persistent infections, latent infections, and transformation.
Term
Persistent infections
Definition
Release of viruses from host cell does not result in cell lysis. The cell remains alive and produces viruses indefinitely.
Term
Latent infections
Definition
Delay between infection by the virus and lytic events.
Term
Transformation
Definition
Conversion of a normal cell into a tumor cell.
Term
Plant Viruses
Definition
Entry often depends on some damage already mead to the plant tissue in order to open a spot in the cell wall.
Term
How can we grow and quantify viruses?
Definition
They are small (can't use a compound microscope) and only replicate in host cells, so strategies are used to amplify and quantify the viruses.
Term
Two types of bacteriophages
Definition
Lytic and lysogenic
Term
Lytic bacteriophage
Definition
Phage will replicate in and burst open (lyse) host
Term
Lysogenic bacteriophage
Definition
Phage can integrate its genome into the host cell (becoming a prophage), and it can be replicated each time the host cell replicates.
Term
Lawn of growth
Definition
Where the cells still are
Term
Plaque
Definition
Indicates cell death / lysis. One virus leads to one plaque, similar to one cell leads to one colony.
Term
Cultivating animal viruses
Definition
Viruses are grown in tissue cultures (usually Hela cells), which must be kept sterile and bacteria-free. CPE can be observed in infected cultured cells.
Term
Viral purification
Definition
1. Simple filtration will remove large cells and cellular debris.
2. Differential centrifugation AND gradient centrifugation
Term
Viral purification: Gradient centrifugation
Definition
Depends on density. Each piece of different density will settle into a different area (or band) of the density gradient after centrifugation.
Term
Virus quantification: direct count
Definition
Electron microscope can be used to visualize a known volume of material, counting the viruses in it and scaling it up to determine the titer.
Term
Problems with direct count
Definition
Expensive, specialized microscope required.
Can't differentiate between infectious and noninfectious viral particles.
Term
Virus quantification: hemagluttination assay
Definition
Exploits the trait of some viruses to stick to red blood cells, causing themto form a gel mat.
Term
Benefits of the hemagluttination assay
Definition
Cheap, easy, fast. No microscope needed.
Term
Problems with the hemagluttination assay
Definition
Some viruses won't work, and it doesn't give an exact number. The assay also doesn't differentiate viable vs. nonviable viruses.
Term
Virus quantitation: endpoint assays
Definition
TCID50 - the amount of virus needed to induce CPE in 50% of culture cells.
LD50 - amount of virus needed to kill 50%of test animal subjects
Term
Types of virus quantitation
Definition
Direct count, hemagluttination assay, endpoint assay
Term
TCID50
Definition
Tissue culture infectious dose 50
Term
LD50
Definition
Lethal dose 50
Term
Ways to name viruses
Definition
Simple letter / number combination; organism they infect; location of discovery; appearance; disease caused
Term
Virus classification: ICTV classification scheme
Definition
Classify based on order,family, subfamily, genus, and species.
Term
Virus classification: The Baltimore classification system
Definition
Developed by David Baltimore. Based around mRNA production methods. Separates viruses into 7 classes.
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