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An overview of viruses, including their characteristics, taxonomy, structure, and replication processes. It covers both dna and rna viruses, as well as enveloped and nonenveloped viruses. The document also discusses the role of viruses in causing diseases and the methods used to identify and culture them.
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Viruses
Biol 240 S
Learning Outcomes
Biol 240 S
3
Characteristics of ALL Viruses
Biol 240 S
General Characteristics of Viruses •^
Most viruses infectonly specific types ofcells in one host
-^
Host range isdetermined by specifichost attachmentreceptors
-^
Polio–
Narrow range
Rabies–
Broad host range
Biol 240 S
7
Viral Proteins
Enzymes–
DNA or RNA Polymerases
-^
protease
Structural Proteins–
Capsid proteins
-^
Receptors
Antigenicity due to differencein structural proteins–
Serotypes
-^
influenza
Antibodies bind to structuralproteins
-^
Cytotoxic T cells
Biol 240 S
Viral Envelope
Components–
Lipoprotein derivedfrom host cell plasmamembrane
-^
Viral proteins
Protein spikes–
Attach to host cellreceptors for hormones
-^
Glycoproteins
-^
Influenza
-^
Hemagglutin
-^
HIV
-^
Gp 120
Less resistant thannon-enveloped viruses
Biol 240 S
9
Viral Taxonomy
Biol 240 S
Viral Taxonomy
Biol 240 S
13
Single Strand RNA Viruses
Enveloped + strand
-^
Togaviridae–
Rubivirus – rubella
Flavivirus–
Yellow fever
Nonenveloped
-^
Picornaviridae–
Rhinovirus
-^
Common cold
-^
Poilovirus
Calciciviridae–
Norovirus
-^
Stomach Flu
Enveloped - strand
-^
Rhabdoviridae–
Rabies
Filoviridae–
Ebola
Orthomyxoviridae–
Influenza
-^
Multiple segments ofsingle stranded RNA
Biol 240 S
14
Culturing Viruses
Viruses must begrown in living cells.
-^
Bacteria–
Phages
Live animals
-^
Embryonated eggs–
Vaccine development
Animal cell cultures
-^
vaccinations
Biol 240 S
Virus
Identification
Biol 240 S
18 Figure 13.10.
5
Capsid
Tail fibers
One Step Growth Curve
Biol 240 S
The Lysogenic Cycle
Figure 13.
Biol 240 S
20
Figure 13.
Prophage exists in galactose-using host(containing the
gal
gene).
Phage genome excises, carryingwith it the adjacent
gal
gene from
the host.Phage matures and cell lyses, releasingphage carrying
gal
gene.
1 2 3
Prophage
gal gal^ gene
gene
Bacterial DNA
Galactose-positivedonor cell
gal
gene
Phage infects a cell that cannot utilizegalactose (lacking
gal
gene).
4
Galactose-negativerecipient cell
Along with the prophage, the bacterial
gal
gene becomes integrated into the newhost’s DNA. 5
Lysogenic cell can now metabolizegalactose. 6
Galactose-positive recombinant cell
Biol 240 S
Animal viruses By budding (envelopedviruses) or rupture
Biol 240 S
24
Figure 13.
Virion attaches to host cell
Virion penetratescell and its DNA isuncoated
Early transcription andtranslation; enzymes aresynthesized
1
2
3
DNA
Late transcription;DNA is replicated 4
Late translation;capsid proteinsare synthesized Virions mature 6 5
Capsid
Papovavirus
Host cell
DNA Cytoplasm
Virions are released 7
Capsid proteins
mRNA
Biol 240 S
+ RNA or SenseStrand = mRNA
Viral genometranscribed
-^
“early proteins”–
Enzymes forviral replication
RdRp–
Synthesizes –stand
-^
template formaking new +strands
“late proteins”–
capsid proteins
Biol 240 S
26
- Strand RNA Viruses - RNA dependent
Biol 240 S
Retrovirus Replication
Figure 13.
Retrovirus penetrateshost cell.
Virion penetratescell and its DNA isuncoated
The new viral DNA istranported into the host cell’snucleus and integrated as aprovirus. The provirus maydivide indefinitely with thehost cell DNA.
1
2
3
DNA
Transcription of theprovirus may also occur,producing RNA for newretrovirus genomes andRNA that codes for theretrovirus capsid andenvelope proteins. 4
Matureretrovirusleaves hostcell, acquiringan envelope asit buds out. 5
Capsid
Reversetranscriptase
Virus
Two identical + stands of RNADNA of one of the hostcell’s chromosomes
Provirus
Hostcell
Reversetranscriptase Viral RNA
RNA
Viral proteins
Identicalstrands ofRNA
Biol 240 S
30
Latent v Persistent Infections
host cell for long periods
long period, generally fatal
(measles virus)
Biol 240 S
Viral Therapy
Pathogen specificbacteriophages
-^
Phages mutate at samerate as bacteria
-^
Selective
-^
Phages multiply insidepatient
-^
Viriotherapy
-^
Oncolytic virusesselectively bind to anddestroy cancer cells
Biol 240 S
32
Prions
Biol 240 S Prions
Figure 13.
PrP
c
PrP
Sc
1
2
3
4
5
6
7
8
Endosome
Lysosome
Biol 240 S
36
th
Biol 240 S
Biol 240 S
Attenuated Whole-Antigen
Vaccines