Virology Flashcards
TERMS AND DEFINITIONS: lipid-containing membrane that surrounds some virus particles Acquired during viral maturation
by a budding process through a cellular membrane.
Envelope
TERMS AND DEFINITIONS: virus particle that is functionally deficient in some aspect of replication.
Defective Virus
TERMS AND DEFINITIONS: Morphologic units seen in the electron microscope on the
surface of icosahedral virus particles.
Capsomeres
TERMS AND DEFINITIONS: protein shell, or coat, that encloses the nucleic acid genome.
Capsid
- smallest infectious agents ranging from about 20nm to
about 300 nm in diameter. - Contains only one kind of nucleic acid (RNA or DNA) as their
genome. - parasites at the genetic level, replicating only in living cells and are inert in the extracellular environment
VIRUSES
PRIONS: SIZE, REPLICATION, CELLWALL, DOMAIN.
Size: EM
Replication: Misfolded proteins causes misfolding of neighboring proteins.
Cellwall: None
Domain: Non- Cellular
VIRUSES: SIZE, REPLICATION, CELLWALL, DOMAIN.
Size: EM
Replication: Nucleic acid replication using host mechanisms.
Cellwall: Protein capsid, some have host cell envelope.
Domain: Non- Cellular
BACTERIA: SIZE, REPLICATION, CELLWALL, DOMAIN.
Size: Micro
Replication: Binary fission
Cellwall: G (+) inner membrane & thick peptidoglycan G (-) inner and outer cell membranes & mid thin peptidoglycan sterols.
Domain: Bacteria
FUNGI: SIZE, REPLICATION, CELLWALL, DOMAIN
Size: Micro to Gross
Replication: Asexual budding, Sexual Mating (Spores)
Cellwall: Ergosterol Chitin cell wall
Domain: Eukaryota
PARASITES: SIZE, REPLICATION, CELLWALL, DOMAIN
Size: Micro to Gross
Replication: Asexual and Sexual
Domain: Eukaryota
TERMS AND DEFINITIONS: Virus-encoded glycoproteins exposed on the surface of the envelope.
Peplomers
TERMS AND DEFINITIONS: proteinβnucleic acid complex representing the
packaged form of the viral genome.
- Term commonly used in cases in which the
nucleocapsid is a substructure of a more
complex virus particle.
Nucleocapsid
TERMS AND DEFINITIONS: basic protein building
blocks of the coat.
usually a collection of more than one non-identical protein subunit. The Protomer - structural unit
Structural units
TERMS AND DEFINITIONS: single folded viral polypeptide chain.
Subunits
TERMS AND DEFINITIONS: complete virus particle; serves to transfer the viral nucleic acid from one cell
to another.
Virion
Classification of Viruses: gene order, number and
position of open reading
frames, strategy of
replication (patterns of
transcription, translation), and cellular sites (accumulation of proteins, virion assembly, virion
release).Classification of Viruses:
Genome organization and replication
Classification of Viruses: number, size, amino acid
sequence, modifications
(glycosylation,
phosphorylation,
myristoylation), and
functional activities of
structural and nonstructural proteins
(transcriptase, reverse
transcriptase, neuraminidase, fusion
activities)
Virus protein properties
Classification of Viruses: reactions to various antisera.
Antigenic properties
Classification of Viruses: molecular mass, buoyant density, pH stability, thermal stability, and susceptibility to physical
and chemical agents,
especially solubilizing
agents and detergents.
Physicochemical
properties of the virion
TERMS AND DEFINITIONS: natural host range, mode
of transmission, vector
relationships,
pathogenicity, tissue
tropisms, and pathology.
Biologic properties
Classification of Viruses: size, shape, type of
symmetry, presence or
absence of peplomers, and presence or absence of
membranes.
Virion morphology
Classification of Viruses: type of nucleic acid (DNA or RNA), size of the genome, strandedness (single or double), whether linear or circular, sense (positive,
negative, ambisense),
segments (number, size),
nucleotide sequence,
percent GC content, and presence of special
features (repetitive
elements, isomerization,
5ΚΉ-terminal cap, 5ΚΉ-terminal covalently linked protein, 3ΚΉ- terminal poly(A)
tract).
Virus genome properties
Types of Symmetry of Virus Particles: Most animal viruses are of icosahedral pattern
Icosahedron β closed shell composed of 20 facets of equilateral triangles, 12 vertices, and fivefold, threefold, and
twofold axes of rotational symmetry
For viruses, these facets are the morphological units and are
usually encoded by the assembly units
Spontaneously assembles into a sphere
Most viruses that have icosahedral symmetry do not have an icosahedral shapeβrather, the physical appearance
of the particle is spherical. Both DNA and RNA viral groups exhibit examples of cubic
symmetry.
E.g., Poliovirus Type 1 (Mahoney strain), adenoviruses
Cubic Symmetry
Types of Symmetry of Virus Particles: Found in filamentous viruses (e.g. Ebola virus, orthomyxoviruses)
- The protein subunits assemble only in
the presence of nucleic acid (unlike
cubic).
-All known examples of animal viruses
with helical symmetry
-contain RNA genomes
-Exception: rhabdoviruses, have flexible
nucleocapsids that are wound into a
ball inside envelopes
Helical Symmetry
Types of Symmetry of Virus Particles: Some viruses have pleiomorphic shapes
and are more
complicated in structure (e.g. poxviruses)
Poxviruses are brick shaped with a
dumbbell structure in the center
Complex Symmetry
Virus Symmetry: These viruses resemble a crystal and are calledicosahedral virus. Example: adenoviruses.
Cubical symmetry
Virus Symmetry: In which the particle is elongated. Most helical viruses are enveloped . Example: influenza virus.
Helical symmetry
Virus Symmetry: In which the viruses are complicated in
structure. Example: poxviruses and bacteriophage.
Complex symmetry
CHEMICAL COMPOSITION OF VIRUSES: All have structural proteins,
some have enzymes
Viral proteins are principal
targets of the immune
response
Proteins
CHEMICAL COMPOSITION OF VIRUSES: DNA or RNA
Single or double-stranded
Positive- or negative -
stranded or ambisense
Ambisense carries negative or positive (Hep B) Contiguous or segmented
Nucleic acids
CHEMICAL COMPOSITION OF VIRUSES: Some viruses have lipid envelopes acquired from the cell in which the virus was produced
Lipids
CHEMICAL COMPOSITION OF VIRUSES: Some viral proteins,
particularly those that
protrude outward, have
carbohydrate groups
These groups often
mediate virus attachment to susceptible cells
Glycoproteins
CULTIVATION AND DETECTION OF VIRUSES: Cell grown in vitro: made by dispersing cells
(Usually with trypsin) fromfreshly removed host tissues. In general, they are unable to
grow for more than a fewpassages in culture
Primary
cultures
CULTIVATION AND DETECTION OF VIRUSES: Cell grown in vitro: made by dispersing cells
(Usually with trypsin) fromfreshly removed host tissues. In general, they are unable to
grow for more than a few passages in culture
Primary
cultures
CULTIVATION AND DETECTION OF VIRUSES: Cell grown in vitro: Diploid cell lines that haveundergone a change that allows their limited culture (up
to 50 passages) but that retain their normal chromosome
pattern.
Secondary
cultures
CULTIVATION AND DETECTION OF VIRUSES: Cell grown in vitro: cultures capable of more
prolonged (indefinite)growth
that have been
derived from diploid cell lines or from malignant tissues. have altered and irregular numbers of chromosome.
Continuous
cell lines
DETECTION OF VIRUS-INFECTED CELLS: cell lysis or necrosis, inclusion body
formation, giant cell
formation, and
cytoplasmic
vacuolization.
(ie, morphologic changes in the cells
Development of cytopathic
effects
DETECTION OF VIRUS-INFECTED CELLS: Specific antisera can be
used to detect the
synthesis of viral
proteins in infected cells.
Ex: hemagglutinin of
influenza virus protein
Appearance of a virusencoded
DETECTION OF VIRUS-INFECTED CELLS: Molecular-based assays
such as polymerase
chain reaction provide
rapid, sensitive, and specific methods of detection
Detection of virus-specific nucleic acid
DETECTION OF VIRUS-INFECTED CELLS: reaction becomes
positive before cytopathic changes are
visible and, in some
cases, occurs in the
absence of cytopathic
effects
Adsorption of erythrocytes
to infected cells, called
hemadsorption, caused by the presence of virusencoded
hemagglutinin
(parainfluenza, influenza) in cellular membranes.
DETECTION OF VIRUS-INFECTED CELLS: result in death of the embryo (eg, encephalitis
viruses), production of
pocks or plaques on the
chorioallantoic membrane (eg, herpes,
smallpox, and vaccinia),
or development of
hemagglutinins in the
embryonic fluids or
tissues (eg, influenza).
Viral growth in an
embryonated chick egg.
IDENTIFICATION OF A PARTICLE AS A VIRUS: prepared against the infectious virus should react with the characteristic particle and vice versa. Direct observation of an unknown virus can be accomplished by
electron microscopic examination of aggregate formation in
a mixture of antisera and crude viral suspension
Antisera
REACTION TO PHYSICAL AND CHEMICAL AGENTS: heat inactivate some viruses, while cold usually preserves them
Heat and cold
REACTION TO PHYSICAL AND CHEMICAL AGENTS:
Many viruses can be stabilized by salts
in order to resist heat inactivation, which is important in the preparation of vaccines
Stabilization by salts
REACTION TO PHYSICAL AND CHEMICAL AGENTS:
- pH Viruses are usually stable between pH
values of 5.0 and 9.0
Some viruses (eg, enteroviruses) are
resistant to acidic conditions.
-All viruses are destroyed by alkaline
conditions.
- Hemagglutination reactions can be
quite sensitive to changes in pH
pH
REACTION TO PHYSICAL AND CHEMICAL AGENTS:
damages nucleic acids; crosslinks viral
Radiation
REACTION TO PHYSICAL AND CHEMICAL AGENTS:
ether is an organic solvent, thus damages envelope membranes of
viruses
Ether susceptibility
REACTION TO PHYSICAL AND CHEMICAL AGENTS:
amphipathic, thus solubilized membranes and can dissociate
noncovalent bonds between viral
proteins
Detergents
REACTION TO PHYSICAL AND CHEMICAL AGENTS:
cross-links nucleic acids and proteins; destroys viral infectivity
Formaldehyde
REACTION TO PHYSICAL AND CHEMICAL AGENTS:
Dyes bind to the viral nucleic acid then
virus becomes susceptible to
Inactivation inactivation by visible light.
Photodynamic
Inactivation
REACTION TO PHYSICAL AND CHEMICAL AGENTS:
Antibacterial antibiotics and sulfonamides have no effect on viruses.
Larger concentrations of chlorine are required to destroy viruses than to kill bacteria, especially in the presence of extraneous proteins.
Antibiotics and Other
Antibacterial antibiotics
