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virus structure - Coggle Diagram
virus structure
structure of virus
1.enveloped vs non enveloped
non-enveloped
only capsid (with spike proteins) + nucleic acid
some naked virus form virus clusters inside vesicles
rotavirus/norovirus that infects GIT
characteristics
more stable in environment
easily transmitted
can survive in adverse conditions, e.g. in gut
can dry out and retain infectivity
release via lysis of host cells
kill host cells
acute infection
enveloped
envelop (with spike proteins) + capsid + nucleic acid
envelop= host derived plasma membrane (phospholipid bilayer)
obtained via budding from the host cells
spike protein= glycoprotein coded by virus
on virus surface for attachment to host cells + entry
characteristics
more fragile than naked virus (with just a capsid)
less stable in the environment (environmentally labile)
easily destroyed by: pH, temp, detergent/disinfectant, drying out, protease
X easily trnasmitted
X survive in adverse conditions, e.g. gut
if envelope=destroyed, no infectivity
coz damage/loss spike proteins needed for attachment and entry
released via budding through host cell membrane
X kill host cells
persistent infection
2.genome composition
DNA
characteristics
All are monopartities (all=have one segment)
little genetic variations
most=double stranded
some genetic material =circular
little structural diversity
RNA
characteristics
can have more than one segments
segmentation of RNA viruses
genetic variations
structural diveristy
most segments only code for single gene in reo and orthomyxo viridae
most are single stranded
except reo and birna viridae
all=linear
need to make own RNA dependent RNA polymerase (RdRp)
to transcript RNA to mRNA
X found in host (host only hv DNA polymerase)
RdRp = error prone
result
short genome
maintain genome from generation to generation
RNA virus= variable
more strains/subtypes/serotypes
zoonoses
evolve rapiadly
RNA virus can readily adapt to new environemnt
reassortment of segments in RNA virus--> increase variations + diversity
process
conifection of the same host by two strains of the same virus
segments from two strains reassort inside the host--> diff/new combination of genes
e.g. influenza, bluetongue
Classification system--Baltimore system
Gp1 (dsDNA)
Gp2 (ssDNA, +ve sense)
Gp3 (dsRNA)
Gp 4 (ssRNA, +ve sense)
Gp 5 (ssRNA, -ve sense)
Gp 6 (ssRNA, +ve sense--> undergo reverse transcription)
Gp 7 (dsDNA, undergo reverse transcription)
3.structure and symmetry of capsid
basic units of capsid
capsomere protein
types
icosahedral
mainly naked
regular, strong, compact
20 triangular sides; 12 vertices
two types of capsomere
penton
hexon
e.g.
parvovirus (naked)
killer dog disease
naked= very stable in environment
helical
must be enveloped
one type of capsomere
spiral configuration of capsid around viral genome
e.g.
paramyxoviridae
canine distemper disease
shape= spherical
rhabdoviridae
Rabies
shape=bullet-shaped
complex
mammalian ones= must be enveloped
assymetrical (X helical or icosahedral)
e.g.
bacteriophage (virus that infects bacteria)
pox virus
smallpox, mouse pox
viral proteins
structural (produced later)
capsid protein
protection of viral genome + uncoating
capsomere self assemble into capsid during replication
naked virus-->capsid contain receptors for attachment and entry
envelope spike proteins
often=glycoprotein
for attachment and entry
targets for host immune system
recognised by antibody
matrix protein
connects envelope and capsid
in virus assembly-->interaction btw envelope and capsid
e.g.
retro, paramyxo, herpse, orthomyxo
only in some virus
virion associated enzyme
RNA dependent RNA virus
esp in all -ve snese RNA virus, need to replicate to form +ve sense RNA (mRNA) before transcription can take place
non-structural (produced earlier)
enzymes involved in replication process
protease
helicase
polymerase (sometimes=structural, e.g. RNA polymerase in -ve sense RNA virus)
regulatory proteins of replication process
oncoproteins
proteins that evade immune response
targets of T cells (coz= epitopes recognised by T cells)
what is virus
obligate intracellular parasite
characteristics
X organelles
use host cellular mechanisms to replicate
Very small, only seen with EM
replicate quickly
Impact of virus
affect animals
deadly
economically costly (culling of infected animals)
zoonotic diseases