Chapter 29 - General Properties of Viruses Flashcards
It is acquired when the viral nucleocapsid buds through a cellular membrane in the course of maturation
Lipid
Lipids in viral membranes are derived from?
Host cell
Occurs only at sites where virus-specific proteins have been inserted into the host cell membrane
Budding
Proteins that are protruding from the envelope and exposed on the external surface of the virus particle
Viral glycosylated proteins
Proteins that are underneath the envelope that anchor the particle together
Viral unglycosylated proteins
Viruses that are sensitive to treatment with ether and other organic solvents
Lipid-containing viruses
Viruses that are generally resistant to ether
Nonlipid-containing viruses
Viral envelopes contain ________
glycoproteins
Enzymes that cleave DNA at specific nucleotide sequences
Restriction endonucleases
The entire infectious unit is termed ________.
virion
True or false. The viruses are inert in the extracellular environment.
True
What encases and stabilizes the viral nucleic acid against the ECE and facilitates the attachment and penetration by the virus
Capsid
The viruses that attack bacteria
Bacteriophages
Morphologic units on the surface of icosahedral virus particles that represent clusters of polypeptides
Capsomeres
A virus particle that is functionally deficient in some aspect of replication
Defective virus
Basic building blocks of the coat
Structural units
A single folded viral polypeptide chain
Subunit
Two theories of viral origin
Derived from DNA or RNA nucleic acid components
Degenerate forms of intracellular parasites
Performed early in virus identification
Genome sequencing
Basis of Classification
- Virion morphology
- Virus genome properties
- Genome organization and Replication
- Virus protein properties
- Antigenic properties
- Physicochemical properties
- Biologic properties
Virus family names have the suffix
-viridae
Genus names carry the suffix
-virus
The ______________________________________ had organized more than 4000 animal and plant viruses
International Committee on Taxonomy of Viruses
Ex. of heavy metal stain to emphasize surface structure
Potassium phosphotungstate
The heavy metal permeates the virus particle like a cloud and brings out the surface structure of viruses by virtue of ___________
“Negative staining”
The typical level of resolution
3-4 nm
Uses virus samples quick frozen in vitreous ice
Cryoelectron microscopy
Can provide atomic resolution info, generally at a level of 0.2-0.3 nm
X-ray crystallography
Types of arrangement of morphologic subunits
Cubic symmetry
Helical symmetry
Complex structures
The most efficient arrangement for subunits in a closed shell
Icosahedral pattern
Describe the icosahedron
20 faces (each an equi triangle), 12 vertices, fivefold, threefold, and twofold axes of rotational symmetry, vertex units have five neighbors (pentavalent) and others six (hexavalent)
How many identical subunits on the surface of an icosahedron
60
Physical appearance of most viruses with icosahedral symmetry
Spherical
Involved in the condensation of the nucleic acid into a form suitable for packaging
Cellular histones
“__________________” on viral nucleic acid are involved in assembly into virus particles
Packaging sequences
Expression of ______ proteins from cloned genes often results in self-assembly and formation of empty virus-like particles.
capsid
Viral architecture where protein subunits are bound in a periodic way to the viral nucleic acid, winding it into a helix
Helical symmetry
True or false. It is possible for “empty” helical patterns to form.
False
All known examples of animal viruses with helical symmetry contain (a. DNA b. RNA) genomes.
b. RNA
Classic attributes of viruses
Small size
Ability to pass through filters
Most widely used method for estimating particle size
Direct observation in the electron microscope
Another method in determining particle size aside from the use of the EM
Sedimentation in the ultracentrifuge
Virus range in diameter from about
20 nm to 300 nm
Particles with a twofold difference in diameter have an ___________ difference in volume
eightfold
What virus has a greater mass, the poxvirus or the poliovirus?
Poxvirus
Their major purpose is to facilitate transfer of the viral nucleic acid from one host cell to another.
Structural proteins
Fxns of structural proteins
- protect the viral genome against inactivation by nucleases
- participate in the attachment of the virus particle to a susceptible cell
- provide the structural symmetry of the virus particle
An enzyme in retroviruses that makes a DNA copy of the viral RNA
Reverse transcriptase
An enzyme carried by viruses with negative-sense RNA genome that is needed to copy the first mRNAs
RNA polymerase
All major (a. DNA b. RNA) viral groups have a linear or circular configuration
a. DNA
True or false. The isolated RNA of the negative-sense RNA viruses is infectious.
False
Hypothesized the existence of infectious agents too small to be seen by a light microscope
Jacob Henle
People responsible for sterile culture
Louis Pasteur and Robert Koch
German; described a non-fungal cause of tobacco mosaic disease; performed limiting dilution and determined that it was not a toxin
Adolf Mayer
Discovered the first filterable human infectious agent in cuba
Walter Reed
Cannot replicate on its own; needs to utilize host cell
Obligate intracellular parasite
genome + capsid
naked virus
genome + capsid + envelope
Enveloped virus
Carrier of genetic material; either RNA or DNA but not both
Genome
Classification of genome
- segmented
- non-segmented
Classification of DNA/RNA
- double stranded
- single stranded
Movement of positive (+) coiling
Counterclockwise
Movement of negative (-) coiling
Clockwise
Icosahedral structure often posses _____ viruses
naked
An example of an enveloped virus having an icosahedral capsid
Herpes virus
May have arisen from transposable elements
Retroviruses
Different wild isolates of the same virus
Strain
Distinct strain of the same virus based upon known genetic difference
Type
A virus that behaves differently in the laboratory than the wild type due to unknown reasons
Variant
