virus 1,2 Flashcards
(26 cards)
what are viruses described as
obligate intracellular parasites
what does obligate intracellular parasites mean
must reproduce in a host cell and use its resources for their own life cycle
properties of viruses
contains own genetic material that replicates inside host cells to reproduce, produces their own proteins/RNA to allow reproduction, host cell supplies the remainder of machinery like ribosomes, larger virus=larger genome=makes more proteins
describe common features of viral particles
-viral genomes packaged into particles, necessary for transmission between hosts
-viral genome contains info for replication within a permissive host cell
-all viruses are obligate intracellular parasites
describe general viral morphology
coverings= capsid, envelope
central core= nucleic acid (DNA/RNA), matrix proteins, enzymes
classify viruses into structure and morphology criterias
-presence or absence of envelope (envelope or naked virus)
-shape of capsid (helical or icosahedral)
describe the difference properties of enveloped and naked viruses
enveloped= sensitive to dryness/heat/detergents/acid, must stay wet to be transmitted, doesnt survive GI tract, envelop is a modified section of host membrane to mask foreignness from host cell
naked= resistant to dryness/heat/detergents/acid/proteases, infective when dry, transmitted via fomites, survives GI tract and environments on surfaces
name the two basic viral shapes
icosahedral and helical
why viral shapes choose icosahedral
nearest geometrical shape to sphere, highest volume to surface ratio, structure built from multiple repetitions of one protein, only one gene needed
what is a capsid and whats it made of
protective shell, protein subunits of capsomeres
describe the helical capsids in plant vs animal viruses
plant- rigid capsule wound into cylinders
animal- flexible capsids loose in envelope
describe capsid in icosahedral virus
capsid forms 3D icosahedron (20 side) with nucleic acid inside, naked or enveloped
how to classify viruses
baltimore classification- viruses grouped based on genomes, predicts replication mechanism, mode of expression, 7 classes
what is the baltimore classification based on
- where virus genome inputs central dogma of molecular biology
- type/nature of nucleic acid
types of nucleic acid
ds-double strand
ss-single strand
+ strand-sense strand
-strand-antisense strand
what is +/-strands
+ strand=sense strand=strand with sequence of mRNA, can be directly read by ribosome to encode protein
- strand=antisense strand=strand complementary to mRNA, needs to be copied to make +strand/mRNA then can be used for translation
what is horizontal transmission
between individuals of the same species by either contact or indirect
contact=direct like blood/sex
indirect=virus spread into environment by infected person, sneezing, second person infected by inhalation
common infection routes
respiratory tract- airborne transmission (aerosols and inhalation) and fomites
GI tract- faecal oral transmission (faecal + ingestion), poor sanitation and hygiene, contaminated food and water, fomites
genital tract- sexual transmission, fluids and skin contact
blood borne viruses- travels through blood to cells, contaminated blood products, needle sharing, accidents (needle stick injury), child birth
what is vertical transmission
between mother and baby/foetuus
what does in utero mean
transplacental infection
what does teratogen viruses mean
mild/no symptoms in mother but causes severe developmental defects or death in child, effects depend on virus and stage of pregnancy
how can viruses be transmitted during delivery
through lesions or fluids
what is viral tropism
specific cell type/tissue/host species that virus can interact and reproduce in, capability of an infectious virus to infect particular cells
what does susceptibility and permissivity mean
susceptibility=host cells that virus can enter
permissivity=host cell that virus can replicate in
