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13-a Viruses13-a Virusespp. 387-415
H1N1
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VirusesViruses
Size, Structure, Morphology
Taxonomy
Growth
Identification
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SMALL size
One type of nucleic acid, either DNA or RNA
Protein coat, surrounds the NA
Few or no enzymes of their own
Characteristics of Viruses
Obligate intracellular parasite
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Multiply inside living host cells by using synthesizing machinery of the cell
Proteins, generate ATP
Specialized structures to transfer viral NA to other cells
Inert Outside Living Host Cells
Significant for development of antiviral drugs
Because most drugs would also interfere with functioning of host cell = toxic
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1. Protein coat (capsids)Capsomeres (make up capsids)
The number varies
The types of protein very
2. Nucleic acids
3. Size
4. Morphology
Can’t use biochemical tests or disease symptoms as for classification
Criteria used to ‘Classify’ Viruses
A virion contains:
6Figure 13.1
SizesSizes
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Viral StructureViral Structure
Nucleic acids
– DNA or RNA is
– Either single or double stranded
– Linear or circular
– In segments
• Example: influenza virus
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Capsid– Protein coat protects nucleic acid
Capsomere – Each capsid composed of protein subunits– Arrangement of capsomeres is characteristic
of a particular type of virusEnvelope (on some viruses)
– Covers the capsidSpikes
– CHO-protein, project from envelope surface for attachment
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1. Helical
2. Polyhedral
3. Enveloped
4. Complex
‘Group’ into several different morphological types
Viral MorphologyViral Morphology
…based on their capsid architecture
• Long rods• Rigid / flexible• NA in center• Diseases:– Ebola hemorrhagic fever– Rabies
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Helical
Fig. 13.4a, b
• Non-enveloped• ‘many sided,’ 20
‘faces’• Icosahedron• Diseases:– Adenovirus– Poliovirus
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Polyhedral
Fig. 13.2
• Covered• Roughly spherical• Enveloped helical• Enveloped polyhedral• Spikes• Diseases:
– Influenza (EH)– Herpes simples (EP)– Flu, fever blisters,
chickenpox, shingles, mononucleosis
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Enveloped
Fig. 13.3
• Bacteriophage• Capsids with
additional structures• Head contains NA• Tail sheath, fibers,
plate, pin• Diseases:– Infect bacteria
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Complex – 1
Fig. 13.5
• Poxvirus• No clearly identifiable
capsids• Have several coats• NA inside the coats• Disease:
– Smallpox
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Complex – 2
Fig. 13.5
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Viral TaxonomyViral Taxonomy
Names Ending
Family -viridae
Genus -virus
Viral species Common names are used for species
Subspecies Designated by a number
Viral species: A group of viruses sharing the same genetic information and ecological niche (host)
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Taxonomy Examples
Names Ending
Family Herpesviridae
Genus Simplexvirus
Names Ending
Family Retroviridae
Genus Lentivirus
Species Human Immunodeficiency Virus
Subspecies HIV-1, HIV-2
1. Provide living cells
2. Viruses that infect bacteria useful for understanding growth
3. Pathogenic viruses difficult to cultivate
1. Can’t use bacteriological media
2. Bacteriophages infect bacteria and grow cultures on plates
3. Grow only in higher primates & humans– Use animal cell culture
techniques
Viral GrowthViral Growth
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• Bacteriophages form plaques on a lawn of bacteria– It’s a virus that infects
bacteria– Plaque is a ‘clearing’
in the bacterial ‘lawn’– Count, PFU’s– PFU: plaque forming
units
Fig. 13.6
Bacteriophage
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• Animal viruses grown in living animals or in embryonated eggs
• Vaccine production
Figure 13.7
Viral Growth in Living Cells
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Animal and plant viruses grown in cell culture
Figure 13.8
Viral Growth in Cell Culture
– Continuous animal cell lines maintained indefinitely
– Famous cell line: HeLa
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Viral Identification – Not EasyViral Identification – Not Easy
1. Too small to see
2. Western blotting
3. Virus kills host cell
4. Restriction fragment length polymorphism
5. Polymerase chain reaction
1. Observe with electron microscope
2. Serological methods
3. Cytopathic effects
4. RFLP’s
5. PCR
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Uninfected (mo) cells Infected (mo) cells, 24 hrs later
Figure 13.9
Cytopathic effect (CPE): a visible effect on a host cell, may result in host cell death; ‘host’ cells deteriorate
Viral Identification – Cytopathic EffectViral Identification – Cytopathic Effect
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Q:Q:
1.Which of the following statements is NOT true?
a.Viruses contain DNA or RNA
b.The nucleic acid of a virus is surrounded by a protein coat
c. Viruses multiply inside living cells using viral mRNA, tRNA and ribosomes
d.Viruses cause the synthesis of specialized infectious elements
e.Viruses multiply inside living cells
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Q:Q:1. In which of the following ways do
viruses differ from bacteria?
a.Viruses are filterable
b.Viruses are obligate intracellular parasites
c. Viruses don’t have any nucleic acid
d.Viruses are not composed of cells
e.All of the above
2. Virus spikes are used for attachment to the host cell. True False
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Q:Q:1. What type of cell is the virus, seen
in the figure, capable of infecting?
a.A liver cell
b.A plant cell
c. A bacterial cell
d.Many different cell types
2. Viruses range in size from 20-1000 nm in length and are easy to see in a compound light microscope.
True False