Post on 07-Feb-2016
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Viruses: Morphology and Bacteriophage Life Cycle
Figure 13.1
What is a Virus and How is it Built?•Obligate intracellular parasites
•Morphology of a Virion•Size (1/1000 to 1/4 size of bacterium)•Composition
•RNA vs DNA•Capsid, envelope, spikes
•Shapes•helical, polyhedral (isometric) , complex
•Host ranges and grouping of viruses•Bacterial, plant, animal viruses
•Propagation and study of viruses•Bacteriophage plaques on a lawn•Animal virus propagation•Identifying viruses
Bacterial Virus Life Cycles (DNA viruses)•Lytic Cycle (e.g. T4 bacteriophage)
•Attachment•Penetration/Entry•Biosynthesis•Assembly•Lysis/Release
•Lysogenic Life CycleViruses cannot reproduce outside of a cell. They are extremely small and come in three different shapes. They are very specific for their hosts. In the lytic cycle of bacteriophages, they enter, reproduce, and leave.
Viruses
Figure 13.1
Helical Viruses
Figure 13.4a, b
Polyhedral (Isometric) Viruses
Figure 13.2a, b
Some Viruses Have a Phospholipid Envelope
Membrane proteinsform “spikes” that stick out from membrane
Complex Viruses
Figure 13.5a
Viral Taxonomy
• “Family” names end in -viridae
• “Genus” names end in -virus
• Viral species: A group of viruses sharing the same genetic information and ecological niche (host). Common names are used for species
• Subspecies are designated by a number
• Herpesviridae
• Herpesvirus
• Human herpes virus 1, HHV 2, HHV 3
• Retroviridae
• Lentivirus
• Human Immunodeficiency Virus 1, HIV 2
Viruses: Morphology and Bacteriophage Life Cycle
Figure 13.1
What is a Virus and How is it Built?•Obligate intracellular parasites
•Morphology of a Virion•Size (1/1000 to 1/4 size of bacterium)•Composition
•RNA vs DNA•Capsid, envelope, spikes
•Shapes•helical, polyhedral, complex
•Host ranges and grouping of viruses•Bacterial, plant, animal viruses
•Propagation and study of viruses•Bacteriophage plaques on a lawn•Animal virus propagation•Identifying viruses
Bacterial Virus Life Cycles (DNA viruses)•Lytic Cycle (e.g. T4 bacteriophage)
•Attachment•Penetration/Entry•Biosynthesis•Assembly•Lysis/Release
Viruses cannot reproduce outside of a cell. They are extremely small and come in three different shapes. They are very specific for their hosts. In the lytic cycle of bacteriophages, they enter, reproduce, and leave.
Growing Viruses
• Viruses must be grown in living cells.
• Bacteriophages form plaques on a lawn of bacteria.
Figure 13.6
• Animal viruses may be grown in living animals, or in embryonated eggs, or in tissue culture
Growing Viruses
• Animal and plants viruses may be grown in cell culture.
• Continuous cell lines may be maintained indefinitely.
Figure 13.8
• Cytopathic effects
• Serological tests
• Detect antibodies against viruses in a patient
• Use antibodies to identify viruses in neutralization tests, viral hemagglutination, and Western blot
• Nucleic acids
• RFLPs (DNA fingerprint)
• PCR (selectively amplifying and detecting key sequences)
Virus Identification
Viruses: Morphology and Bacteriophage Life Cycle
Figure 13.1
What is a Virus and How is it Built?•Obligate intracellular parasites
•Morphology of a Virion•Size (1/1000 to 1/4 size of bacterium)•Composition
•RNA vs DNA•Capsid, envelope, spikes
•Shapes•helical, polyhedral, complex
•Host ranges and grouping of viruses•Bacterial, plant, animal viruses
•Propagation and study of viruses•Bacteriophage plaques on a lawn•Animal virus propagation•Identifying viruses
Bacterial Virus Life Cycles (DNA viruses)•Lytic Cycle (e.g. T4 bacteriophage)
•Attachment•Penetration/Entry•Biosynthesis•Assembly•Lysis/Release
Viruses cannot reproduce outside of a cell. They are extremely small and come in three different shapes. They are very specific for their hosts. In the lytic cycle of bacteriophages, they enter, reproduce, and leave.
Figure 13.10.1
Attachment:Phage attaches to host cell.
Penetration:Phage pnetrates host cell and injects its DNA.
Biosynthesis: Transcription/Translation andViral chromosome replication
1
2
3
Bacterial cell wall
Bacterial chromosome
Capsid DNA
Capsid
Sheath
Tail fiber
Base platePin
Cell wall
Tail
Plasma membrane
Sheath contracted
Tail core
Lytic Lifecycle of a Bacteriophage I
Figure 13.10.2
4 Maturation/Assembly:Viral components are assembled into virions.
Tail
5 Release:Host cell lyses and new virions are released.
DNA
Capsid
Tail fibers
Lytic Lifecycle of a Bacteriophage II
Lytic Life Cycle Overall
The Lytic and Lysogenic Cycles
Figure 13.12
Viruses: Morphology and Bacteriophage Life Cycle
Figure 13.1
What is a Virus and How is it Built?•Obligate intracellular parasites
•Morphology of a Virion•Size (1/1000 to 1/4 size of bacterium)•Composition
•RNA vs DNA•Capsid, envelope, spikes
•Shapes•helical, polyhedral, complex
•Host ranges and grouping of viruses•Bacterial, plant, animal viruses
•Propagation and study of viruses•Bacteriophage plaques on a lawn•Animal virus propagation•Identifying viruses
Bacterial Virus Life Cycles (DNA viruses)•Lytic Cycle (e.g. T4 bacteriophage)
•Attachment•Penetration/Entry•Biosynthesis•Assembly•Lysis/Release
•Lysogenic Life CycleViruses cannot reproduce outside of a cell. They are extremely small and come in three different shapes. They are very specific for their hosts. In the lytic cycle of bacteriophages, they enter, reproduce, and leave.