Viruses Flashcards
describe the basic biology of viruses
simple acellular infectious pathogens
incapable of self replication or metabolic activity
obligate intracellular parasites
describe the viral genome
can be DNA or RNA
can be linear or circular
can be single stranded or double stranded
what does +sense and -sense mean in viral genomes?
in linear RNA it can be be either
+sense (mRNA) can be read for protein synthesis as it is
-sense has to be converted into +sense
what are the components of the nucleocapsid?
nucleic acid + capsid (+ possible accessory enzymes)
can also be naked or enveloped
define a virion
fully assembled infectious extracellular particle
what is the capsid composed of and what is their symmetry?
composition - capsomeres (several grouped polypeptides)
symmetry - helical or icosahedral
what are enveloped viruses characterised by?
phospholipid bilayer derived from host cells
what can the host cell bilayer be derived from?
plasma membrane, golgi, ER and nuclear membrane
what are enveloped viruses composed of?
lipids, virus proteins and glycoproteins
what are host cell membranes replaced by?
virally encoded glycoproteins (spike proteins)
what do viruses express to facilitate host entry?
glycoproteins
capsid proteins (in naked viruses)
anchored in phos. bilayer (in enveloped viruses)
what is viral tropism?
ability of a given virus to productively infect a particular cell, tissue or host species
name 6 different modes of viral transmission?
oral transmission, droplet transmission, direct inoculation, sexual transmission, trans-plascental, direct skin contact
name the 7 core structures found in a typical virus
envelope membrane, capsid/shell, enzymes, matrix protein, transport channels, genome/nucleic acid, transmembranous glycoprotein spikes
name some examples of respiratory illnesses caused by viruses
viral pneumonia, bronchiotitis, common cold
what is a zoonoses?
an infection passed from a non-human host to a human host
what are some key features of human herpesviruses?
persist for the lifetime of the host
remain latent (non replicating)
what kind of virus is HIV?
single stranded +sense RNA retrovirus
what is macropinocytosis?
where the virus attaches to the host cell and is engulfed by the host cell membrane
what is membrane fusion?
where the virus inserts itself into the host cell
what can occur after a viral infection?
virus can be released out of host
virus can be maintained in host cell cytoplasm
virus can be incorporated into genome
virus can become oncogenic
why do viruses show genome variation?
evolutionary pressure from host immune system or antiviral drugs
what 3 mechanisms can cause viral genome variation?
mutation, recombination, gene switching/reassortment
what characteristics of a virus can influence the rate of mutation?
RNA viruses mutate faster than DNA viruses
single stranded mutates faster than double stranded
smaller viral genomes mutate faster than larger
what 3 mutation types are common in viral mutations?
insertion, deletion and substitution
what enzyme is required to replicate RNA viral genomes?
RNA dependant RNA polymerase
under what conditions can recombination/reassortment occur in viruses?
if 2 strains of a virus infect the same host
define viral genome recombination
the exchange of entire genes between the 2 strains
define viral gene reassortment
the exchange of entire segments of genome between strains
what is the difference between antigenic drift and antigenic shift?
antigenic drift - gradual change in genetic makeup
antigenic shift - sudden change in genetic makeup
