Transcript Viruses of Bacteria

Chapter 13 and 14--- Virus
Preview
• Characteristics of virus
• Basic structure of virus
• Life cycle of virus (virulent and
temperate)
• Replication of viral genome
• Culture virus
Viruses - General Information
Two general groups:
1. Those that infect eukaryotic cells
2. Those that infect prokaryotic cells
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Referred to as bacteriophage, or phage
Used as a model to understand animal viruses
Mechanism of DNA transfer
Used to destroy bacteria
Viral particle
(virion)
Nucleic acid inside a
protein coat
Host cell
Release of many viral
particles
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.
Viruses - General Information
Too small to see using a
light microscope
Figure 13.1
Viral Architecture
Genome surrounded by a protein coat (capsid)
nucleocapsid
naked virus
generally more resistant
generally eukaryotic viruses only
Viral Architecture
Genome surrounded by a protein coat (capsid)
phage
Viruses - General Information
Viruses multiply only within a host cell
•Utilize the host cell’s machinery (viruses lack the ability to
harvest energy, synthesize proteins)
•Direct that machinery to produce more viral particles
Viral particle
(virion)
Nucleic acid inside a
protein coat
Host cell
Release of many viral
particles
Viral Interaction with Host Cells
Viral particle
Host cell
Productive infection
Viral particles released via:
Lysis of host cell (lytic infection)
Extrusion from host
Latent infection
Release of many viral
particles
burst size
Viral Interaction with Host Cells
Viral particle
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
Viral Interaction with Host Cells
Viral particle
Host cell
Productive infection
Viral particles released via:
Lysis of host cell (lytic infection)
Extrusion from host
repressor
Latent infection
Viral genome resides silently within host prophage/provirus
Infected bacterial cell is referred to as a lysogen
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
Bacteriophage Infections
Infection Process (productive)
T4
Attachment - via specific
receptors on host; lack of
receptor  resistance
Infection Process (productive)
T4
Penetration - genome is
injected into cell
Infection Process (productive)
T4
Transcription/translation
early proteins - ex. nucleases
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
Infection Process (productive)
T4
Assembly - self-assembly
Infection Process (productive)
T4
Release - often lysis,
sometimes extrusion (lytic
phages lyse cells)
Lambda
Latent infections
Temperate phage
Two options:
1) Lytic cycle
2) Lysogenic cycle
Integration/replication
Phage “senses” stresslevel of host
Lambda
Latent infections
Immunity of lysogens
repressor
Lysogenic conversion
Transduction
DNA is transferred via a bacteriophage
Generalized transduction - lytic or temperate phage
Specialized transduction - temperate phage only
Generalized Transduction
Initial steps of a
typical productive
infection
Phage-encoded
nuclease degrades
host DNA
Generalized Transduction
Initial steps of a
typical productive
infection
Phage-encoded
nuclease degrades
host DNA
Wild-type phage
Error in
packaging
Transducing particle
carries bacterial DNA
Generalized Transduction
Initial steps of a
typical productive
infection
Error in
packaging
Phage-encoded
nuclease degrades
host DNA
Generalized Transduction
Initial steps of a
typical productive
infection
Error in
packaging
Phage-encoded
nuclease degrades
host DNA
Specialized Transduction
Initial steps
generate a lysogen
lysogen
•begins lytic cycle
•incorrect excision
Specialized Transduction
Initial steps
generate a lysogen
lysogen
•begins lytic cycle
•incorrect excision
• Only DNA that flanks the site of
integration can be excised with phage
DNA
• Some phage genes are left behind
Specialized Transduction
defective phage
Initial steps
generate a lysogen
lysogen
•begins lytic cycle
•incorrect excision
Lytic cyle:
•replication of phage parts
•assembly
•release
Specialized Transduction
defective phage
Initial steps
generate a lysogen
lysogen
•begins lytic cycle
•incorrect excision
Viruses that Infect Animal
Cells
Infection Process
Attachment
Penetration
•fusion with the host membrane (enveloped viruses only)
Infection Process
Attachment
Penetration
•fusion with the host membrane (enveloped viruses only)
•endocytosis
Replication
•genome
•protein synthesis
Assembly
Release
•Cell death  lysis
•Budding
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
Acute Infections
Persistent Infections
shingles
Replication of the Genome
ds DNA
ss DNA
Central dogma
Replication of the Genome
initial template
DNA polymerase
final product
ds DNA
ss DNA
ATCCGTA
TAGGCAT
ATCCGTA
Replication of the Genome
initial template
ds DNA
ss DNA
+ strand
- strand
DNA polymerase
final product
Replication of the Genome
ds RNA
ss RNA
Replication of the Genome
Long ds RNA signifies to our cells that they are virally-infected
RNA-dependent RNA polymerase
Virally-encoded
enzyme (replicase)
initial template
final product
ds RNA
ss RNA
(+) strand (mRNA)
(-) strand
5’
3’
3’
5’
(-) ss and ds RNA vir. must bring own replicases  made during prev. infec.
Replication of the Genome
Retroviruses - ss (+) RNA  ds DNA ss (+) RNA
Reverse transcriptase
DNA copy integrates into the host
cell’s genome
Replication of the Genome
Retroviruses - ss (+) RNA  ds DNA ss (+) RNA
Reverse transcriptase
Virally-encoded enzymes
Target for antiviral drugs
ex. AZT - nucleotide analog
Error-prone ( mutations)
DNA copy integrates into the host
cell’s genome
Growing Bacteriophage in the
Laboratory
Lawn of host cells
Plaques
Growing Eukaryotic Viruses in
the Laboratory
Tissue culture
Growing Eukaryotic Viruses in
the Laboratory
Tissue culture
Growing Eukaryotic Viruses in
the Laboratory
Tissue culture