Virology Flashcards
Define a virus
Infectious, obligate intracellular parasite comprising of genetic material surrounded by a protein coat
What do viruses use host cell machinery for
To replicate the viral genome and produce viral proteins
Viruses do not replicate by division - what do they do
Assemble from proteins and genomes formed from the host cell machinery
Describe what a virus is like outside of a host cell
Inert / Inactive
In host cells what do viruses turn the host cells into
Virus factories
What is a virion
Complete infectious viral particle
What is a capsid and what is its function
A protein coat - it protects the viral genetic material
What do capsids self assemble from
Multiple copies of structural proteins
Name given to an individual protein subunit of a capsid
Protomer
What makes up a nucleocapsid
Capsid + Viral nucleic acid
Describe a helical capsid
Hollow tubes with protein walls and the nucleic acid sits on the inside
Describe a Icosahedral capsid
20 triangular faces arranged around the surface of a sphere constructed of pentamers or hexamers
Name given to cells with and without an envelope
Enveloped and naked
What are viral envelopes made of and how are they accquired
Lipo-protein bilayer
When virus buds through host cell-plasma membrane
What is the function of spike proteins
Involved in viral attachment to host cell antigenic site / host’s cell receptors
If enzymes are present in viruses what is their function
Involved in replication of viral nucleic acids
The viral genome can go 1 of 2 ways in 5 senses - what are they
DNA or RNA
ds or ss
linear or circular
continuous or segmented
ss can be + or -
What does each segment code for in the viral genome
A protein
By convention what ss is +
mRNA
What has to happen to the viral genome to enable translation into proteins by host ribosomes
It needs to be converted to mRNA
6 stages of viral replication
- Attachment to host cell via specific receptor
- Entry into host cell
- Uncoating - liberation of viral genome from viral protein coat
- Synthesis of proteins and replication of viral genome
- Self-assembly of nucleocapsids
- Release from the cell host
How are steps 1 and 6 different for enveloped and non enveloped cells
Enveloped - Endocytosis or membrane fusion - budding
Non-enveloped - Endocytosis - lysis
The viral envelope is normally formed from the host’s PM but what else can it be made from
Golgi apparatus
ER
What are the 3 classification of viruses
DNA viruses
RNA viruses
Retro-transcribing viruses
What has to happen to ssDNA before translation
Must be converted into dsDNA
What enzyme do RNA viruses use
RNA-dependent RNA polymerases (RdRp)
What 2 enzymes do retro transcribing viruses use
Reverse transcriptase (RT)
Integrase
How are virus names written
Lower case and without italic
What are 2 techniques used to measure the number of infectious viral particles
Plaque assay
End point dilution assay
What are 2 techniques used to measure the number of viral particles
Electron microscopy
ELISA - viral proteins
qPCR - viral genome
What does a plaque assay allow
Determination of the virus titre (concentration) in a sample
What are plaques
Circular zone of lysed (dead) cells
Why do you cover the cells in agar during a plaque assay
To restrict diffusion of virus particles
What does end-point dilution assay allow
Determination of the dilution of a virus required to infect 50% of inoculated cell cultures
During the 1 step growth cycle how do you ensure that infection is synchronous
Short exposure to a high number of virions
What can the 1 step growth cycle be used to analyse
Virus and host factors that facilitate viral replication
What are the 3 periods in the 1 step growth cycle
Eclipse - no infectious viral particles
Burst - huge amplification in short amount of time
Plateau - no production of infectious viral particles
6 routes of infection in humans (3 tracts)
Eye - conjunctiva
Respiratory tract
Gastrointestinal tract
Urogenital tract
Skin - must be breached
Placenta in pregnant woman
4 main routes of infection - ACVV
Airborne, contact, vehicle and vector
What is horizontal and vertical transfer of disease
H - person to person
V - mother to unborn child
What is a viral pantropism
Where a virus can infect all tissues
Why does apoptosis stop viral replication
Viruses cannot replicate in a dead cell
What does a cell performing apoptosis form
Blebs
What is autophagy - what is formed and what is it discarded by
Cytoplasmic content is degraded by a formation of a membrane - autophagosome and phagocytosed by a lysosome
Cells must be accessible, susceptible and permissive for successful initiation of infection - what do these mean
Accessible - no protection from physical barrier
Susceptible - appropriate receptor on surface
Permissive - contain correct molecules for viral replication
What defences need to be overcome for initiation of infection
Antiviral defences
What are the 4 routes can viral diseases take when acute
Death
Clearance and recovery
Chronic then death
Chronic then latent (replication can be replicated)
Where does replication occur after successful infection (2)
Site of entry or primary site
Name for when a virus is in the blood
Viremia
When is a virus considered a systemic spread
When is reaches the secondary site
Word for when viral infection leads to uncontrolled replication
Oncogenesis
Non-cell death effect of viruses on cells
Interference with normal cellular functions
Give an example of these defences
Anatomical and chemical
Intrinsic
Innate
Acquired
A+C - skin and mucus
I - Apoptosis and autophagy
I - Cytokinesis
A - T and B lymphocytes
2 defence strategies cells use
Neutralising viral particles
Prevention of intracellular replication
2 examples of indirect defence strategies
Apoptosis and autophagy
What are PRRs and what do they recognise
Pattern recognition receptors - viral nucleic acids
PRRs activate transcription factors that transcript what 2 things
IFN - interference
Inflammatory cytokines
What do inflammatory cytokines lead to the secretion of
sentinel cells
2 examples of sentinel cells - what are their general role
Dendritic cells and natural killer cells
Patrol tissues looking for signs of change
Give 2 ways dendritic cells are activated - where do they go
Viral proteins released from infected cells
Apoptotic bodies
Lymph nodes
What do dendrites bridge in the immune response
Innate to adaptive response
When type 1 interferons are secreted what receptors do they bind to and where are they found
Type 1 IFN receptors on infected cells or neighbouring cells
When Type 1 IFNs bind to the receptors this triggers a signalling cascade which leads to the expression of what and what effect does this gene have
Interferon stimulated gene
Anti-viral effect
Give 2 examples of adaptive responses to viruses
Cytotoxic T lymphocytes
Neutralising antibodies
What is reduced on the cell surface of infected cells that CTLs can recognise
MHC-1
Why are regulators of IFN and cytokines necessary
To avoid pathology
What are symptoms of a viral disease a consequence of
Host response to infection
2 reasons for immunopathology
Uncontrolled innate immune response
Damaging effects of adaptive immune response
