Viruses: Morphology and Bacteriophage Life Cycle
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 Cycle
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 13.1
Viruses
Figure 13.1
Helical Viruses
Figure 13.4a, b
Polyhedral (Isometric) Viruses
Figure 13.2a, b
Some Viruses Have a Phospholipid Envelope
Membrane proteins
form “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
• Retroviridae
• Herpesvirus
• Lentivirus
• Human herpes
virus 1, HHV 2,
HHV 3
• Human
Immunodeficiency Virus
1, HIV 2
Viruses: Morphology and Bacteriophage Life Cycle
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 13.1
Growing Viruses
• Viruses must be
grown in living
cells.
• Bacteriophages
form plaques on a
lawn of bacteria.
• Animal viruses
may be grown in
living animals, or
in embryonated
eggs, or in tissue
culture
Figure 13.6
Growing Viruses
• Animal and plants viruses may be grown in cell
culture.
• Continuous cell lines may be maintained
indefinitely.
Figure 13.8
Virus Identification
• 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)
Viruses: Morphology and Bacteriophage Life Cycle
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 13.1
Lytic Lifecycle of a Bacteriophage I
Bacterial
cell wall
Bacterial
chromosome
Capsid
DNA
Capsid
Sheath
Tail fiber
1 Attachment:
Phage attaches
to host cell.
Base plate
Pin
Cell wall
Tail
Plasma membrane
2 Penetration:
Phage pnetrates
host cell and
injects its DNA.
Sheath contracted
Tail core
3 Biosynthesis:
Transcription/
Translation and
Viral
chromosome
replication
Figure 13.10.1
Lytic Lifecycle of a Bacteriophage II
Tail
DNA
4 Maturation/Assembly:
Viral components are
assembled into
virions.
Capsid
5 Release:
Host cell lyses and
new virions are
released.
Tail fibers
Figure 13.10.2
Lytic Life Cycle Overall
The Lytic and Lysogenic Cycles
Figure 13.12
Viruses: Morphology and Bacteriophage Life Cycle
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 Cycle
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 13.1