Basic Virology Flashcards
Virus
Slimy liquid poison; substance produce by the body as tge result of disease, especially one that capable of infecting others
Viruses may have arisen from:
- Mobile genetic elements that gain the ability to move between cells
- May be descendats of previously living organisms
- Derived from DNA or RNA nucleic acid of host cells that become able to replicate autonomously and evolve independently
- Degenerate formd of intracellular parasites
Showed that a disease im tobacco was caused by a virus
1890, Ivanovski and Beijerinck
Discovered an animal virus that causes foot and mouth disease in cattle
1890, Loeffler and Frosch
Viruses that infected a bacterium
Bacteriohage or phages * They are needed for transduction
Viral growth cycle
*Viruses cannot replicate on their own
The period between the infection and the appearance of a matured virus in the cell *Virion
Eclipse period
Composed of regular, repeating subunits that gives rise to its crystalline appearance. Contain only those parts that it needed to invade and control host cell
Molecular structure
External coating
Capsid *Envelope- in 13 of the 20 families of animal viruses
no envelope
Naked virus
core
DNA (double stranded)
RNA (single stranded)
capsid + nucleic acid
Nucleocapsid
fully formed virus that can establish an infection in a host cell
Virion
Capsid is constructed from identical subunits called?
capsomers
types of capsid
Helical, Icosahedral, Complex
take a bit of the host cell membrane to form an envelope
enveloped viruses
In the envelope, some or all of the regular membrane proteins are replaced with
viral proteins
Some proteins form a___________ between the envelope and the capsid
binding layer
Glycoproteins remain exposed as spikes; essential for attachment
peplomers
Functions of the Viral Capsid/Envelope
- Protect nucleic acids.
- Help introduce the viral DNA or RNA into a suitable host cell.
- Stimulate the immune system to produce antibodies that can protect the host cells against future infections.
at the core of the virus
Nucleic acid
the sum total of the genetic information carried by an organism
genome
exceptions to the rule
Parvoviruses contain single-stranded DNA
Reoviruses contain double-stranded RNA
DNA viruses
- ssDNA
- dsDNA
dsDNA
Linear, and circular
genomes that are ready for immediate translation into proteins
positive-sense RNA
genomes have to be converted into the proper form to be made into proteins
Negative-sense RNA
individual genes exist on separate pieces of RNA
segmented
the gold standard in the identification
molecular methods; genetic sequencing
OTHER SUBSTANCES IN THE VIRUS PARTICLE
- ENZYME
for specific operations within the host cell
OTHER SUBSTANCES IN THE VIRUS PARTICLE
POLYMERASES
to synthesize DNA and RNA
OTHER SUBSTANCES IN THE VIRUS PARTICLE
REPLICASES
to copy RNA
- Structure
- Chemical composition
- Similarities in genetic makeup
MAIN CRITERIA
International Committee on the Taxonomy of Viruses, 2000
3 orders
63 families “-viridae”
263 genera “-virus”
7 GROUPS IN BALTIMORE’S CLASSIFICATION
- Double stranded DNA viruses
- Single stranded DNA viruses
- Double stranded RNA viruses
- Positive sense single stranded RNA viruses
- Negative sense single stranded RNA viruses
- Single stranded reverse transcribing RNA viruses
- Double stranded reverse transcribing DNA viruses
I, II, VII
DNA viruses
ENVELOPED VIRUSES
Poxviridae (complex) – linear
Herpesviridae – linear, icosahedral, toroid
Hepadnaviridae – circular
NONENVELOPED dsDNA
Adenoviridae – linear, icosahedral
Papovaviridae – circular, icosahedral
NONENVELOPED ssDNA
Parvoviridae
- Virus encounters susceptible host cells
- Adsorbs specifically to receptor sites on the cell membrane
Because of the exact fit required, viruses have a limited host range
ADSORPTION
Exact fit:
Exact fit: Lock and key model or goodness of fit model
- Flexible cell membrane of the host is penetrated by the whole virus or its nucleic acid
- Endocytosis: entire virus engulfed by the cell and enclosed in a vacuole or vesicle
- The viral envelope can also directly fuse with the host cell membrane
PENETRATION
- Enzymes in the vacuole dissolve the envelope and capsid
- The virus is now uncoated
UNCOATING
Free viral nucleic acid exerts control over the host’s synthetic and metabolic machinery
SYNTHESIS
SYNTHESIS AND REPLICATION OF DNA VIRUSES
NUCLEUS
DNA enters the nucleus and is transcribed into RNA
The RNA becomes a message for synthesizing viral proteins (translation)
New DNA is synthesized using host nucleotides
SYNTHESIS AND REPLICATION OF RNA VIRUSES
CYTOPLASM
Mature virus particles are constructed from the growing pool of parts
ASSEMBLY
RELEASE!
Nonenveloped and complex viruses are released when ?
the cell lyses or ruptures
Enveloped viruses are liberated by?
EXOCYTOSIS OR BUDDING
HOW MANY VIRIONS MAY BE RELASED?
3,000 TO 100,000
ENTIRE LENGTH OF CYCLE
8-36 HOURS
DAMAGE TO THE HOST CELL AND PERSISTENT INFECTIONS
virus-induced damage to the cell that alters its microscopic appearance
CYTOPATHIC EFFECTS
compacted masses of viruses or damaged cell organelles
INCLUSION BODIES
Response in Animal Cell
Virus
Cells round up; inclusions appear in cytoplasm
Smallpox virus
Cells fuse to form multinucleated syncytia; nuclear inclusions
Herpes simplex
Clumping of cells; nuclear inclusions
ADENOVIRUS
Cell lysis; no inclusions
POLIOVIRUS
Cell enlargement; vacuoles and inclusions in cytoplasm
REOVIRUS
Cells round up; no inclusions
INFLUENZA VIRUS
No change in cell shape; cytoplasmic inclusions (Negri bodies)
RABIES VIRUS
Syncytia form (multinucleate)
Measles virus
Some viral infections maintain a _________ wherein the cell harbors the virus and is not immediately lysed
CARRIER RELATIONSHIP
from a few weeks to remainder of the host’s life
PERSISTENT INFECTIONS
SLOW VIRUSES
Some viruses remain in __________, periodically becoming activated
a chronic latent state
Herpes viruses and Varicella-Zoster virus (VZV)
Some viruses enter their host cell and _______ its genetic material, leading to cancer
PERMANENTLY ALTER
Oncogenic viruses
Their effect is called transformation
mammalian viruses capable of initiating tumors
ONCOVIRUSES
VIRUSES THAT INFECT BACTERIA
- Bacteriophages
- Most contain dsDNA
- Often make the bacteria they infect more pathogenic for humans
- Icosahedral capsid head containing DNA
- Central tube surrounded by a sheath
- Collar
- Base plate
- Tail pins
- Fibers
T-EVEN PHAGES
special DNA phages that undergo adsorption and penetration but are not replicated or released immediately
Instead, the viral DNA enters an inactive _________
TEMPERATE PHAGES ; PROPHAGE STAGE
the cell’s progeny will also have the temperate phage DNA
Lysogeny
when a bacterium acquires a new trait from its temperate phage
LYSOGENIC CONVERSION
