virology intro Flashcards
Viruses versus cellular organisms
theories of viral origin
reductive
intracellular
independent
reductive theory of viral origin
intracellualr parasite infects cell and reduces the amt of genetic material it possesses to a form a DNA virus
intracellular origin of viruses
functional parts of cell that acquired the ability to reproduce themselves uncontrolled by the cell, formed retroviruses
independent origin of viruses
viroid nucleic acids evolved outside the cells in the “RNA world” and acquired ability to infect cells
size of viruses
smaller than bac
largest virus
pandoravirus
multicomponent viruses
Multicomponent viruses genomes are segmented and the segments are distributed into separate viral particles
infection by multicomponent viruses
multiple distinct particles are required for infection
Cultivation of viruses requires:
examples?
what might you see?
inoculation of living host cell • suitable animals • embryonated eggs • tissue (cell) cultures – monolayers of animal cells
plaques= localized area of cellular destruction and lysis
• cytopathic effects (CPEs)
– microscopic or macroscopic degenerative changes or abnormalities in host cells and tissues
basic viral structure
delivery system and a payload
Delivery system = structural components that enable the virus to survive and bind host cells
Payload = viral genome and enzymes required for initial steps of replication
naked capsid and envolped viruses strucutres
Icosahedral symmetry
famous virus with Icosahedral symmetry
HSV-1 (herpes)
tails of viruses
may be present to attach to host cells
helical symmetry
nucleic acid coated with proteins in a helical conformation
ebola has what symmetry
helical symmetry
Enveloped vs. nonenveloped viruses structures (with the different symmetry too)
Asymmetrical viruses
genome with no symmetry, usually surrounded with capsid or membrane
vaccina pox virus symmetry
asym
Main groups of human RNA viruses
Main groups of human DNA viruses
Viruses are classified using a combination of properties:
- Type and structure of nucleic acid used for viral genome
- Presence or absence of envelope
- Type of capsid symmetry
- Replication strategy
Virus Replication steps
–adsorption –penetration and uncoating –synthesis of viral proteins and nucleic acids –assembly of virions –release
Adsorption of Virions
• viral surface proteins and/or enzymes mediate attachment to specific host receptors
Penetration and Uncoating
• three mechanisms
– injection of nucleic acid
– fusion of envelope with host membrane
– endocytosis
injection of NA
envelope fusion mechanism
endocytosis penetration by virus mechanism
single-stranded +RNA viruses
pro synthesis and genome replication
single-stranded -RNA viruses
pro synthesis and genome replication
double-stranded RNA viruses
pro syn and DNA replication
retroviruses
pro syn and genome replication
hepadnaviruses
pro syn and genome replication
single-stranded DNA viruses
pro syn and genome replication
double-stranded DNA viruses
pro syn and genome replication
double-stranded DNA viruses
pro syn and genome replication
Assembly of Virus Capsids
capsid pro encoded by?
naked vs enveloped viruses
site?
• capsid proteins
– encoded by late genes
• assembly of naked viruses
– empty procapsids formed then nucleic acid inserted
• assembly of enveloped viruses
– in most cases, similar to assembly of naked viruses
• site of morphogenesis varies
Virion Release of naked viruses
usually by lysis of host cell
virion release of enveloped viruses
– formation of envelope and release usually occur concurrently
• virus-encoded proteins incorporated into host membrane
• nucleocapsid buds outward and is surrounded by modified host membrane
Virus replication events during a single infectious cycle
titer level during the events?
release occurs during assembly as well
Typical transcription pattern for a DNA virus
early genes for replication/pro syn
late genes for exit
possible Pathobiology of viral diseases
Viral encounter and entry
respiratory GI/ Oral lesion blood/body fluid insect bites
bacteriophages part of?
human virome, bind various receptors
possible cycles of bacteriophage reproduction
lysis/ lysogeny
slow release
lytic cycle of bacteriophage reproduction
phage inserts DNA to host cell, can cyclize into circular form cell synthesizes capsid proteins replication of phage DNA DNA packaged into capsids cell is lysed an progeny are released
lysogeny cycle of bacteriophages
occurs when condition are favorable, cell is not lysed
phage DNA inserted into host genome and replicated when cell divides= produces population with phage genome present
lysogeny to lytic cycle transition
stress may induce the excision of phage DNA
DNA can recombine to form circular form and enter lytic cycle
phage c1 provides gene for
botinulum toxin
beta phage provides gene for
diptheria toxin
epsilon 34 provides gene for
LPS synthesis
HERV-W retrovirus provides the gene for?
placental fusion
HERV-E retrovirus provides the gene for?
liver function
slow release of bacteriophage
will maintain cell, cell divides more slowly though due to resources being used to make phages
DNA inserted, forms a circle
DNA replicated
phages assembled and exit without lysis
cell reproduces slowly during this
bacterial defenses against phages
Genetic resistance – mutations in bacterial genes (e.g. receptor)
Restriction endonucleases – enzymes that cut invading DNA
CRISPR – a bacterial immune system
CRISPR
viral DNA injected into bacteria is cleaved and a spacer is formed in the genome
later infection causes expression of spacers into crRNAs that associated with CAS enzyme
allows CAS to target viral DNA= destroy it
phage assistance with bacterial infections and immune reactions
possible treatments?
being explored as a possible antibiotic replacement
