Chapter 13 and 14--- Virus

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Chapter 13 and 14--- Virus
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Preview

• Characteristics of virus
• Basic structure of virus
• Life cycle of virus (virulent and temperate)
• Replication of viral genome
• Culture virus

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Viruses - General Information
Two general groups

• Those that infect eukaryotic cells
• Those that infect prokaryotic cells
• Referred to as bacteriophage, or phage
• Used as a model to understand animal viruses
• Mechanism of DNA transfer
• Used to destroy bacteria

Nucleic acid inside a protein coat
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FDA Consumer magazine January-February
2007 Bacteria-Eating Virus Approved as Food
Additive By Linda Bren Not all viruses harm
people. The Food and Drug Administration has
approved a mixture of viruses as a food additive
to protect people. The additive can be used in
processing plants for spraying onto ready-to-eat
meat and poultry products to protect consumers
from the potentially life-threatening bacterium
Listeria monocytogenes (L. monocytogenes). The
viruses used in the additive are known as
bacteriophages. Bacteriophage means "bacteria
eater." A bacteriophage, also called a phage
(pronounced fayj), is any virus that infects
bacteria.
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Viruses - General Information
Too small to see using a light microscope
Figure 13.1
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Viral Architecture
Genome surrounded by a protein coat (capsid)
nucleocapsid
naked virus
generally more resistant
generally eukaryotic viruses only
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Viral Architecture
Genome surrounded by a protein coat (capsid)
phage
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Viruses - General Information
Viruses multiply only within a host cell

• Utilize the host cells machinery (viruses lack
  the ability to harvest energy, synthesize
  proteins)
• Direct that machinery to produce more viral
  particles

Nucleic acid inside a protein coat
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Viral Interaction with Host Cells
burst size
Productive infection Viral particles released
via Lysis of host cell (lytic infection)
Extrusion from host Latent infection
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Viral Interaction with Host Cells
Host cell
Productive infection Viral particles released
via Lysis of host cell (lytic infection)
Extrusion from host Latent infection Viral
genome resides silently within host
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Viral Interaction with Host Cells
Host cell
Productive infection Viral particles released
via Lysis of host cell (lytic infection)
Extrusion from host Latent infection Viral
genome resides silently within host
repressor
prophage/provirus
Infected bacterial cell is referred to as a
lysogen
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Viral Genome
Encodes proteins that Make up the viral
particle (ex. protein coat) Assure replication of
viral nucleic acid Enable viral particles
(virions) to exit host cell, then enter
another Genome consists of RNA or DNA (not
both), double-stranded or single-stranded
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Bacteriophage Infections
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Infection Process (productive)
T4
Attachment - via specific receptors on host lack
of receptor ? resistance
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Infection Process (productive)
T4
Penetration - genome is injected into cell
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Infection Process (productive)
T4
Transcription/translation early proteins - ex.
nucleases
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Infection Process (productive)
T4
Replication of phage Replication of phage genome
Transcription/translation early proteins-
nuclease, enzymes involves in phage DNA
replication. late proteins - capsid proteins,
lysozymes
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Infection Process (productive)
T4
Assembly - self-assembly
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Infection Process (productive)
T4
Release - often lysis, sometimes extrusion (lytic
phages lyse cells)
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Latent infections
Lambda

• Temperate phage
• Two options
• Lytic cycle
• Lysogenic cycle

Integration/replication Phage senses
stress-level of host
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Latent infections
Lambda
Immunity of lysogens
repressor
Lysogenic conversion
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(No Transcript)
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Transduction
DNA is transferred via a bacteriophage
Generalized transduction Specialized transduction
- lytic or temperate phage
- temperate phage only
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Generalized Transduction
Initial steps of a typical productive infection
Phage-encoded nuclease degrades host DNA
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Generalized Transduction
Initial steps of a typical productive infection
Phage-encoded nuclease degrades host DNA
Error in packaging
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Generalized Transduction
Initial steps of a typical productive infection
Phage-encoded nuclease degrades host DNA
Error in packaging
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Generalized Transduction
Initial steps of a typical productive infection
Phage-encoded nuclease degrades host DNA
Error in packaging
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Specialized Transduction
Initial steps generate a lysogen
lysogen

• begins lytic cycle
• incorrect excision

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Specialized Transduction
Initial steps generate a lysogen

• Only DNA that flanks the site of integration can
  be excised with phage DNA
• Some phage genes are left behind

lysogen

• begins lytic cycle
• incorrect excision

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Specialized Transduction
Initial steps generate a lysogen

• Lytic cyle
• replication of phage parts
• assembly
• release

lysogen

• begins lytic cycle
• incorrect excision

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Specialized Transduction
Initial steps generate a lysogen
lysogen

• begins lytic cycle
• incorrect excision

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Viruses that Infect Animal Cells
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Infection Process

• Attachment
• Penetration
• fusion with the host membrane (enveloped viruses
  only)

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Infection Process

• Attachment
• Penetration
• fusion with the host membrane (enveloped viruses
  only)
• endocytosis

• Replication
• genome
• protein synthesis
• Assembly

• Release
• Cell death ? lysis
• Budding

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Infection Process

• Attachment
• Penetration
• fusion with the host membrane (enveloped viruses
  only)
• endocytosis

• Replication
• genome
• protein synthesis
• Assembly

• Release
• Cell death ? lysis
• Budding

acquisition of envelope
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Acute Infections
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Persistent Infections
shingles
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Replication of the Genome
Central dogma
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Replication of the Genome
ds DNA
ss DNA
TAGGCAT
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Replication of the Genome
ds DNA
ss DNA strand - strand
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Replication of the Genome
ds RNA
ss RNA
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Replication of the Genome
Long ds RNA signifies to our cells that they are
virally-infected
RNA-dependent RNA polymerase
ds RNA
ss RNA
() strand (-) strand
(mRNA)
(-) ss and ds RNA vir. must bring own replicases
? made during prev. infec.
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Replication of the Genome
Retroviruses - ss () RNA ? ds DNA? ss () RNA
Reverse transcriptase
DNA copy integrates into the host cells genome
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Replication of the Genome
Retroviruses - ss () RNA ? ds DNA? ss () RNA
Reverse transcriptase
DNA copy integrates into the host cells genome
Virally-encoded enzymes Target for antiviral
drugs ex. AZT - nucleotide analog Error-prone (?
mutations)
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Growing Bacteriophage in the Laboratory
Lawn of host cells Plaques
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Growing Eukaryotic Viruses in the Laboratory
Tissue culture
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Growing Eukaryotic Viruses in the Laboratory
Tissue culture
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Growing Eukaryotic Viruses in the Laboratory
Tissue culture