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Lecture 2

Lecture 2 CSB351 Virology

2 Pages
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Department
Cell and Systems Biology
Course Code
CSB351Y1
Professor
Mounir Abou Haidar

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Definition of Virus
Viral particles formed of one or several molecules of nucleic acids: RNA OR DNA, but never both
{
Virus: icosahedral or helical shaped (RNA not in the hole of the loop but is packed inside the helix
{
Capsid/coat is to protect virus: most viruses have capsid --> some viruses may exist without
{
Some viruses are parasite of other viruses: Hep D (human) is parasite of HepB --> steals capsid protein
{
Virus, consisting of genetic material enclosed in a protective coating
¾
¾
No metabolic system, no intrinsic motility, cannot respond to stimuli, do not grow in the usual sense--> EXCEPTION: one
bacteria virus (tail part contracts, virus injects DNA into bacteria)
¾
Ability to maintain genetic continuity, with possibility for mutation, is the only basis for considering viruses to be ALIVE
¾
Viruses: in ever single living organism--> ubiquitous
¾
HIV: retrovirus--> different: take their genetic info (RNA), convert into DNA, which goes into nucleus of the cell,
integrate into chromosome and stay there --> viral genetic information becomes a PART of genetic info of the cell
|
All other types: don't go near the nucleus--> go into cytoplasm of the cell, makes millions of copies of their own
gene then virus particle and then burst through the cell
|
Virus integrates piece of DNA near oncogene (normal genes in human cells involved in cell division--> most of
these, proto-oncogenes,usually turned off after embryonic stage)--> viral DNA integration re-activate oncogene-->
continuous/unstoppable cell division--> cancer (i.e. Cervix cancer)
|
The genes added to cell by the virus cause the infected cell to either produce more virus particles (end result cell death)
or to change characteristics of the cell (cancerous)
¾
Goodheart (1969):
{
Nature of Virus
Particles formed of one or several molecules of nucleic acids: RNA or DNA but not both
{
Several= Divided genome--> i.e. Influenza virus (several pieces of RNA)
One= single genome--> i.e. Polio, TMV
CAPSID: genome usually (but not necessarily) covered by one or several types of protein
{
Envelope: some viruses, on top of having capsid protein, also have envelope
{
Polio virus, Norwalk
¾
Most ___ plant viruses are not enveloped
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Enveloped: HIV, Herpes, Rabis
¾
Not all viruses are enveloped:
Influenza virus: i.e. H1N1
¾
HA = glycoprotein (protein + sugar attached) --> used as receptor-binding for the virus: recognize some molecule (sialic
acid) on the surface of the cell to ATTACH--> virus is endocytosed by the cell --> replicates in the cell, makes lots of
copies, infection--> virumia= lots of virus in the blood--> FEVER: immune system makes Ab
NA = neuraminidase --> exactly like sialic acid, but functions to cut virus and release them from the cell, so they can go
and infect other cells
Virus: before get released from cell, spike into their lipid bilayer the VIRAL NA and HA --> virus then detach and signal
LIPID: viruses take it from the cell they infect --> through budding
Smaller: bacteria 1 micron, viruses 30 000 to make up 1mm
¾
Simpler
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Unable to multiply outside a living cell --> Absolute Parasitism
¾
Viruses are:
{
Nucleic acid: RNA/DNA carries genetic information, to code for diff genes of the virus
¾
Genome = set of genes
All viruses must code for at least 1 protein: polymerase (few exceptions) --> synthesis of new RNA/DNA of the virus; all
also code for their coat/capsid proteins to cover and protect their genetic material + form the virus particle
Here: must take nucleotides from the cell's machinery --> cannot synthesize their own nucleotides
Protein: i.e. TMV only 1 protein making helical structure
¾
Lipids: not all have this
¾
Carbohydrates
¾
Cations: K+1, Ca+2, Mg+2
¾
Nucleic acid = sugar + base + phosphate
RNA/DNA: -charged due to phosphate groups (normally have + charged histones to neutralize this)
Virus: grabs some cations from the cell to neutralize
Composition of viruses:
{
Structure:
{
Sperhical/icosahedral
Helical/rod shaped
Combination
Replication:
{
Lecture 2 Definition of Virus
September-17-09
1:26 PM
CSB351 Course Notes Page 1
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Description
Lecture2 Definition of Virus September-17-09 1:26 PM DefinitionofVirus { Viralparticlesformedofoneorseveralmoleculesofnucleicacids:RNAORDNA,butneverboth { Virus:icosahedralorhelicalshaped(RNAnotintheholeoftheloopbutispackedinsidethehelix { Capsidcoatistoprotectvirus:mostviruseshavecapsid-->somevirusesmayexistwithout { Somevirusesareparasiteofotherviruses:HepD(human)isparasiteofHepB-->stealscapsidprotein { Goodheart(1969): Virus,consistingofgeneticmaterialenclosedinaprotectivecoating Oneofthesimplestentitiestoreproduce Nometabolicsystem,nointrinsicmotility,cannotrespondtostimuli,donotgrowintheusualsense-->EXCEPTION:one bacteriavirus(tailpartcontracts,virusinjectsDNAintobacteria) Abilitytomaintaingeneticcontinuity,withpossibilityformutation,istheonlybasisforconsideringvirusestobeALIVE Viruses:ineversinglelivingorganism-->ubiquitous Thegenesaddedtocellbytheviruscausetheinfectedcelltoeitherproducemorevirusparticles(endresultcelldeath) orto changecharacteristicsofthecell(cancerous) HIV:retrovirus-->different:taketheirgeneticinfo(RNA),convertintoDNA,whichgoesintonucleusofthecell, integrateintochromosomeandstaythere-->viralgeneticinformationbecomesaPARTofgeneticinfoofthecell Allothertypes:dontgonearthenucleus-->gointocytoplasmofthecell,makesmillionsofcopiesoftheirown genethenvirusparticleandthenburstthroughthecell VirusintegratespieceofDNAnearoncogene(normalgenesinhumancellsinvolvedincelldivision-->mostof these,proto-oncogenes,usuallyturnedoffafterembryonicstage)-->viralDNAintegrationre-activateoncogene--> continuousunstoppablecelldivision-->cancer(i.e.Cervixcancer) Natureof Virus { Particlesformedofoneorseveralmoleculesofnucleicacids:RNAorDNAbutnotboth Several=Dividedgenome-->i.e.Influenzavirus(severalpiecesofRNA) One=singlegenome-->i.e.Polio,TMV { CAPSID:genomeusually(butn
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