Download Viruses, Prions - De Anza College

13-a Viruses
pp. 387-415
H1N1
Viruses
Size, Structure, Morphology
Taxonomy
Growth
Identification
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Characteristics of Viruses
Obligate intracellular parasite
SMALL size
One type of nucleic acid, either DNA or RNA
Protein coat, surrounds the NA
Few or no enzymes of their own
3
Inert Outside Living Host Cells
Multiply inside living host cells by using
synthesizing machinery of the cell
Proteins, generate ATP
Specialized structures to transfer viral NA to other
cells
Significant for development of antiviral drugs
Because most drugs would also interfere with
functioning of host cell = toxic
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Criteria used to ‘Classify’ Viruses
A virion contains:
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
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for classification
Sizes
Figure 13.1
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Viral 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 virus
Envelope (on some viruses)
– Covers the capsid
Spikes
– CHO-protein, project from envelope surface
for attachment
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Viral Morphology
‘Group’ into several different morphological types
…based on their capsid architecture
1.
2.
3.
4.
Helical
Polyhedral
Enveloped
Complex
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Helical
•
•
•
•
Long rods
Rigid / flexible
NA in center
Diseases:
– Ebola hemorrhagic
fever
– Rabies
Fig. 13.4a, b
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Polyhedral
• Non-enveloped
• ‘many sided,’ 20
‘faces’
• Icosahedron
• Diseases:
– Adenovirus
– Poliovirus
Fig. 13.2
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Enveloped
•
•
•
•
•
•
Covered
Roughly spherical
Enveloped helical
Enveloped polyhedral
Spikes
Diseases:
– Influenza (EH)
– Herpes simples (EP)
– Flu, fever blisters,
chickenpox, shingles,
mononucleosis
Fig. 13.3
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Complex – 1
• Bacteriophage
• Capsids with
additional structures
• Head contains NA
• Tail sheath, fibers,
plate, pin
• Diseases:
– Infect bacteria
Fig. 13.5
13
Complex – 2
• Poxvirus
• No clearly identifiable
capsids
• Have several coats
• NA inside the coats
• Disease:
– Smallpox
Fig. 13.5
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Viral Taxonomy
Names
Family
Genus
Viral species
Subspecies
Ending
-viridae
-virus
Common names are used for
species
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
Family
Genus
Ending
Herpesviridae
Simplexvirus
Names
Family
Genus
Species
Subspecies
Ending
Retroviridae
Lentivirus
Human Immunodeficiency Virus
HIV-1, HIV-2
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Viral Growth
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
Bacteriophage
• 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
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Viral Growth in Living Cells
• Animal viruses
grown in living
animals or in
embryonated
eggs
• Vaccine
production
Figure 13.7
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Viral Growth in Cell Culture
Animal and plant viruses grown in cell
culture
– Continuous animal cell lines
maintained indefinitely
– Famous cell line: HeLa
Figure 13.8
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Viral Identification – Not Easy
1. Observe with
electron microscope
2. Serological methods
1. Too small to see
3. Cytopathic effects
4. RFLP’s
5. PCR
3. Virus kills host cell
4. Restriction fragment
length polymorphism
5. Polymerase chain
reaction
2. Western blotting
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Viral Identification – Cytopathic Effect
Uninfected (mo) cells
Infected (mo) cells, 24 hrs later
Cytopathic effect (CPE): a visible effect on a host cell, may result in host cell death;
‘host’ cells deteriorate
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Figure 13.9
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:
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:
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
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