13 Virus 1 Flashcards
what are viruses
obligate intra-cellular parasites
what surrounds a virus
nucleic acid surrounded by protein capsid or protein shell
how do viruses enter cells
via interaction with specific cell receptors = TROPISM
what happens when a virus enters a cell
following cell enter the host cell machinery is hijacked = synthesis of new virus
how is a virus released
released by budding (enveloped virus) or by cell lysis or via secretory pathway
what is an orphan virus
virus that doesn’t result in disease
virion
virus particle
Virus structure - nucleic acid
can be DNA or RNA
nucleocapsid
nucleic acid plus protein
how are capsids arranged
arranged in symmetrical patterns
HIV structural arrangement
HIV has helical nucleocapsid and icosahedral core
what have some viruses developed from host cell membrane
some viruses also possess a lipid envelope derived from host cell membrane
what are some viruses involved in
involved in cell attachment and entry
what are some of the enzymatic functions viruses have
> for copying viral genome (polymerases)
for trimming viral proteins (proteases)
other modifying enzymes
how are viruses grouped
according to their shared properties nature of the nucleic acid: RNA or DNA capsid symmetry presence or absence of an envelope size
how are virus families named
All Families have the suffix -viridae (e.g. retroviridae), whilst genera have suffix virus (e.g. flavivirus)
hierarchy of recognized viral taxa
(Order) > Family > (Sub-family) > Genus > Species
Not all viruses belong to a order or sub-family
RNA viruses
Take RNA put into cell and get a virus back
Use own polymerase to make a positive sense copy
what do viruses lack
mitochondria and ribosomes
what is used to replicate the viruses
polymerases required to replicate their nucleic acid genome (be it DNA or RNA)
where can virus replication occur
only in living cells
what mediates virus attachment to target cells
mediated by a specific interaction between a component (usually a protein) of the surface of the virus and a cellular receptor
what is the capsid sometimes covered in when buds
sometimes the capsid is covered with the membrane of the host cell as the virus buds off
how does a virus enter
Attachment and replication - Interaction with specific cell surface receptor
> Membrane fusion
- Receptor-mediated endocytosis
what is receptor-mediated endocytosis
take things from outside of the cell and bring into inside
Genome replication and virus protein production - RNA virus
virion contents: (-)RNA dsRNA (+)RNA genome replication cycle RNA to RNA
Genome replication and virus protein production - reverse-transcribing viruses
virion contents:
(+)RNA
dsDNA
genome replication RNA to DNA using reverse transcriptase
Genome replication and virus protein production - DNA virus
virion contents:
ssDNA
dsDNA
genome replication DNA to DNA
Virus release
Nucleocapsid assembly may take place in nucleus or cytoplasm
Envelope viruses bud through cell membrane (sometimes through golgi / ER)
Non-enveloped viruses mature in golgi / cytoplasm
- transported to surface via secretary vesicles
May or may not cause cell lysis
Bacteriophage
Lytic phage
Temperate phage
Pseudolysogeny
Lytic phage
phage genome replicated, phage capsid and tail proteins are synthesized using bacterial cell machineries; the phage genome is then packaged into progeny phage particles, which are liberated via bacterial lysis
Temperate phage
phage genome integrated into bacterial chromosome (becoming a prophage)
persists as a latent or dormant phage
Prophages replicated together with bacterial host chromosome during host cell replication and switch into lytic production upon exposure to DNA damage
Pseudolysogeny
bacterial cells can’t support DNA replication or protein synthesis
phage genome remains for extended period of time as a non-integrated preprophage, at which point the phage enters either a lysogenic or a lytic life cycle
when does pseudolysogeny occur
nutrient-deprived conditions
why does pseudolysigenic preprophage not replicate
Pseudolysogenic preprophage does not replicate and so is only inherited by one of the daughter cells following cell division
Tobacco mosaic virus
ssRNA +ve
Tobacco mosaic virus effect
causes mottling of leaves and fruits and affects tomatoes peppers cucumbers as well as tobacco
what do human viruses usually cause
cell death and inflammation - damage to respiratory tract cells and aching body and fever as the inflammatory response of the immune system reacts to the virus proteins
what do some latent infections cause
initial infection goes away but later a further sometimes slightly different infection breaks out from virus stored in the body- such as human Herpes viruses which cause chicken pox and shingles
what is sputnik
Virophage virus that requires another virus to replicate inside the amoeba
retrovirus advantages
effective over long periods
efficient transfection ex vivo
low immune response in host
retrovirus disadvantages
small, max 8kb insert size
inefficient transfection in vivo
relies on target cell mitosis
safety concerns
retrovirus type
integrates with host chromatin
lentivirus advantages
transfects proliferating and non-proliferating hosts and haemo stem cells
new generation are self-inactivating for safety
lentivirus disadvantages
need active transport into cell
small, max 8kb insert size
technologically challenging
safety concerns, immunodeficiency origins
adeno-associated virus advantages
very good length of expression especially in vivo
efficient transfection in vivo
low immune response in host
adeno-associated virus disadvantages
safety problems owing to potential insertional mutagenesis
small, max 4.5kb insert size
high immuno response
technologically challenging
adeno-associated virus type
either
adenovirus advantages
highly efficient transfection in vivo and ex vivo
transfects proliferating and non-proliferating hosts
adenovirus disadvantages
repeat treatments ineffective due to strong immune response
small, max 7.5kb insert size
technologically challenging
short expression duration
adenovirus type
extra chromosomal DNA
herpes simplex virus advantages
very good length of expression especially in vivo
safe for use in immunocompromised patients
large insert size up 30kb
effective on many cell types
herpes simplex virus disadvantages
difficult to produce in large quantities
herpes simplex virus type
extra chromosomal DNA
