Viruses Flashcards
what is a virus?
simple acellular infectons pathogens, incapable of self replication or metabolic activity.
what is the average size of a human virus?
20 to 200nm can’t be seen under light microscope
what are the possibilities of viral genomes?
-DNA or RNA
-linear or cellular
-single stranded or double stranded (not for circular RNA)
what are some viral components?
-genome (nucleic acids)
-capsid (protein coat)
-nucleocapsid (complete unit of nucleic acid and capsid)
-naked or enveloped
capsid?
surrounds the genome ,composed of capsomeres, several different polypeptides grouped together. distinctive symmetry.
what is a virion?
fully assembled infectious ectracellular particle
what are the two types of capsid structures?
helical and isocahedral
what are enveloped viruses?
characterised by a phospholipid bilayer derived from the host cell ;
-plasma membrane
-golgi
-ER
-nuclear membrane
what are enveloped viruses composed of?
-lipids
-virus proteins and glycoproteins
what are glycoproteins?
they are expressed by viruses and help facilitate host cell entry. they are host cell receptor specific
where are glycoproteins expressed?
-alongside capsid proteins in naked viruses
-anchored in the phospholipid bilayer of enveloped viruses
what is viral tropism?
ability of a virus to productively infect a
-particular cell
-tussue
-host species
what are some modes of transmissions?
-droplet
-direct
-sexual
-transplacental
direct skin contact
oral
how can viruses be classified?
sie
genetic material
capsid structure and symetry
naked or enveloped
what are some diseases caused by viruses?
-respiratory illness (cold bronchitis, croup, viral pneumonia)
-coronaviruses
-influenzas
-herpes
-MMR
-HIV/AIDS
-ebola
-zica
what is a zoonoses?
infection passed from a non human host to a human host
what are the classifications of herpes?
-cold sores
-chicken pox
-shingles
what is a normal CD4 count?
450-1600
how do viruses enter a cell?
generally by endocytosis
what is macropinocytosis?
once the virus attaches to the host cell it can become engulfed by the host cell membrane
what is membrane fusion?
when the virus inserts itself into the host cell
what are the stages that are essential for virus replication?
-attatchemnt
-penetration
-uncoating
-replication
-assembly
-virion release
penetration?
-attatchment to specific receptor which can induce a conformational change in viral capsid proteins or the lipid envelope
-results in the fusion of viral and cellular membranes
-some DNA viruses can also enter by receptor mediated endocytosis
uncoating?
viral capsid is removed and degraded by viral enzymes or host enzymes releasing the viral genomic nucleic acid
replication?
-transcription or translation
-differs between DNA and RNA viruses with opposite polarities
-culminates in the de novo synthesis of viral proteins and genome
assembly?
-after de novo synthesis
-viral proteins packaged with newly replicated viral genome in new virions ready for release from host cell
virion release?
-lysis or budding
-lysis results in death of infected Jost cell (cytolytic viruses)
-budding results in the acquisition of the viral phospholipid envelope, don’t kill host cell (cytopathic)
persistent?
the virus may be maintained in the host cell cytoplasm eg herpes
what are the outcomes of viral infection?
-virus can be released and destroyed by cell lysis
-can exit by budding
-maintained in host cytoplasm
-become incorporated in genome
-can become oncogenic
what are the 3 molecular mechanisms that can cause viral genome variation?
-mutation
-recombintion
-gene switching/reassortment
what are some examples of mutations?
-insertion
-deletion
-substitution
what affects the rate of mutation?
-RNA faster that DNA
-SS faster than DS
-smaller genomes faster than larger
what is recombination?
exchange of entire genes between two strains, if two strains infect a host, recombination will occur confusing it resulting antigenic shift
antigenic drift?
small mutations within antigenic genes over time which allows viruses to evade host immune systems
what is antigenic shift?
an abrupt major change in virus
what is the distinctive feature of coronaviruses?
spikes on their surfaces
how many droplets does a cough produce?
3,000
how many droplets does a sneeze produce?
40,000
what are the types of influenza?
A, B and C
A+B cause significant human disease
B+C have limited genetic diversity and almost occur extensively in human
A is a zoonosis
what causes chicken pox?
varicella zoster virus
what causes cold sores?
herpes simplex virus
what are the symptoms of measles?
-onset is flu like illness with high fever
-cough
-conjunctivitis
-red spots with bluish white centre in lining of cheeks inside
-widespread rash
what is rubella?
important cause of preventable congenital defects
-infecton occurs in early pregnancy
-can result in miscarriage and still births
-highest risk of cogenital infection is during first 12 weeks
when is HIV recognised as turning to AIDS?
when CD4 count drops below 200cells/mm3
how does HIV infect an individual?
spreads through bodily fluids and attacks immune system and CD4+ cells
what are the symptoms of Zika virus?
-fever
-rash
-headache
-joint pain
-conjunctivitis
-muscle pain
what is congenital zika syndrome?
passed from mother to child during pregnancy
-microcephaly (small head) in the child
-reduces their brain size
-associated with guillian barre syndrom
what are the possibilities of the nucleic acid genome of a virus?
RNA OR DNA
genome may be circular or linear
continuous or segmented
double stranded or single stranded
what are some examples of enveloped viruses?
herpes
HIV
example of a non enveloped/ naked virus?
polio
what is positive sense viral RNA?
similar to mRNA and thus can be immediately translated by the host cell
what is negative sense viral RNA?
complementary to mRNA and thus must be converted to positive sense RNA by an RNA polymerase before translation
what is the function of a capsid?
provides protection for the viral genome against environment and functions in receptor recognition
how do viruses enter the host cell?
generally by a form of endopinocytosis
what is macropinocytosis?
once the virus attached to the host cell it can become engulfed by the host cell membrane
what is membrane fusion?
where the virus inserts itself into the host cell
what are the 6 basic stages of virus infection?
-attatchment
-penetration
-uncoating
-replication
-assembly
-virion release
what is budding?
results in acquisition of the viral phospholipid envelope. these types of virus do not usually kill the infected cell and are termed cytopathic viruses
what transcribes the first strand of the RNA double stranded virus?
viral polymerase into mRNA
what does it mean to have a single strand positive sense?
the same base sequence as that is required for translation, it can be used directly as mRNA
what does it mean to have a negative sense configuration ?
must be first transcribed using viral polymerase into a positive sense strand, which can then act as mRNA.
how is a positive sense single strand RNA transcribed?
first made into a negative sense single strand DNA using viral reverse transcriptase carried in nucleocapsid
double stranded DNA then formed which enters the nucleus and becomes integrated in the host genome
integrated viral DNA is then transcribed by host polymerase into mRNA
how does HIV invade immune cells?
infects T cells via high affinity interactions between the virion envelope glycoprotein (gp120) and the CD4 molecule. infection of the T cells is assisted by the T cell co receptor CXCR4 while HIV infects monocytes by interacting with the ccr5 co receptor
what is the innate immune response to a viral infection?
recognition of PAMPS BY PRRs
pro inflammatory cytokines and interferons
which herpes virus causes cold sores
herpes simplex
Wha does positive sense mean?
Their genome RNA can be translated directly ask mRNA
What are the three enzymes within the capsid of HIV that are essential for replication, function and survival?
Integrase, reverse transcriptase, protease
which virus is commonly associated with antigenic shift?
influenza A
which herpes virus causes chicken pox
varicella zoster virus
where does the varicella zoster virus (chicken pox) remain after the skin infection heals?
nerve cells
what is shingles a reinfection from?
chicken pox (varicella zoster virus)
