POS - Virology Flashcards
What is a virus?
An obligate intrcellular parasite
What does it need?
A host cell
What are the details?
Very small - need electron microscope to visualise
Lacks organelles - no nucleus, mitochondria or ribosomes
What is the structure of a naked/un enveloped virus?
Capsid surrounding viral nucleic acid and viral enzymes
What is the structure of an enveloped virus?
Lipid bilayer with viral envelop protein surrounds the capsid
This surrounds the viral nucleic acid and viral enzymes
What is the virus envelope made of?
Host derived lipid bilayer
Virus encoded glycoproteins, which form spikes and protrude from virus surface.
How do you classify a virus with its structure?
Genome structure and composition
Structure and symmetry of the capsid
Presence or absence of an envelope
How do you split viruses depending on their genome?
DNA - double stranded DNA virus or single stranded DNA virus with some circular.
RNA - double stranded RNA or single stranded RNA. This ssRNA then splits to positive - translated directly to proteins or negative - has to be translated to positive before translated to proteins.
Whats an example of ssDNA viruses?
Parvoviridae
Circoviridae
Whats an example of dsDNA viruses?
Poxviridae
Herpesviridae
Papillomaviridae
Adenoviridae
Papovaviridae
What are DNA viruses?
All monopartite (all viral genes on a single segment)
Mostly ds
Few circular
Little diversity
What are RNA viruses?
Mostly ss
All linear
Can have more than one segment
What are examples of dsRNA?
Reoviridae
Birnaviridae
What are examples of +ve ssRNA?
Coronaviridae
Picornaviridae
Arteriviridae
Flaviviridae
What are examples of -ve ssRNA?
Paramyxoviridae or Orthomyxoviridae
What enzyme do RNA viruses need to take with them?
RNA polymerase to copy the genome so are dependent
Why are RNA polymerases error prone and what are the consequences of this?
No proof reading and this makes the viruses more variable and able to evolve rapidly.
Why are RNA viruses segmented?
To allow reassortment to increase diversity
eg. bluetongue and influenza
How do RNA viruses reassort?
Mix genes during replication, requiring simultaneous infection of different strains
2 strains of different virus infect and due to reassortment there can be new progeny.
What are the three types of capsid structure?
Icosahedral
Helical
Complex
What is the icosagedral capsid look like?
Regular, strong and compact
12 vertices, with 20 triangular sides (5,3 and 2 symmetry)
Composed of capsomers
Most without envelop
What is a capsomer?
The basic building block of a capsid made of repeating protein units.
Either penton or hexon.
What is an example of a non-enveloped icosahedral virus?
Parvoviridae
12 capsomers, 60 copies 3 proteins VP2. Extremely stable
What is a helical capsid?
A single capsid protein in a spiral configuration. All are enveloped.
What is an example of an enveloped helical capsid virus?
Paramyxoviridae - ssRNA, spherical and much larger e.g. canine distemper
Rhabdoviridae - bullet shaped with spike like projections e.g. rabies
What is a complex capsid?
Asymmetrical and neither helical or ocosahedral
Whats an example of a complex capsid virus?
Pox viruses - large enveloped dsDNA, brick shaped or ovoid virion e.g. orf.
What are naked viruses?
Icosahedral capsid e.g. adenovirus
What are enveloped viruses?
Few icosahedral e.g. icosahedral
All helical are enveloped e.g helical
Mammalian complex are enveloped e.g. pox
What are characteristics of enveloped viruses?
Pleomorphic ( not regular shape)
Has host derived lipid bilayer and embedded viral glycoproteins
Contain receptors needed for virus entry
How do enveloped viruses aquire an envelope?
As they bud through the host membrane (except poxvirus)
How are naked viruses released?
By lysis
What are the biological properties of enveloped viruses?
More fragile so more easily destroyed by GIT, detergents, disinfectants and outside environment.
Needs to stay wet so not likely spread
Cause persistent infections (doesnt kill cell)
Needs receptors on the envelop to enter
What are the biological properites of unenveloped viruses?
Environmentally stable to temp, drying out, pH, detergents and proteases.
Easily spread and can survive drying out.
Has to kill cell via lysis
What are structural viral proteins?
Capsid proteins
Envelope proteins
Matrix protein (layer inside envelope and outside capsid)
Virion-associated enzyme
What are non-structural proteins/
Often enzymes involved in replication cycle
Some regulatory proteins, oncoproteins etc.
What is the function of virus capsid proteins?
Protect the viral nucleic acid
Capsids contain receptors that attach to host cell to allow entry
What are the function of virus envelope proteins?
Often glycosylated, embedded proteins.
Contain preceptors to attach to a permissive host cell receptor
Targes of host immune response
Interact with capsid during virus assembly
What are the function of viral matrix proteins?
Connects envelope with the virus capsid.
Crucial in interaction and assembly
Found in paramyxovirus, orthomyxoviruses, herpesvirus and retrovirus
What is the function of enzymes that are structural proteins?
RNA viruses carrying own RNA polymerase as a structural protein
Seen in all -ve sense RNA viruses
What is the function of non structural viral proteins?
Made in virus-infected cell, often enzymes involved in viral replication (proteases, helicases, polymerase and protein primers)
Help proteins avoid host immune response
Targets T cell epitopes.
