1. 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

2. Viruses
Figure 13.1

3. Helical Viruses
Figure 13.4a, b

4. Polyhedral (Isometric) Viruses
Figure 13.2a, b

5. Some Viruses Have a Phospholipid Envelope
Membrane proteins
form “spikes” that
stick out from membrane

6. Complex Viruses
Figure 13.5a

7. 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

8. 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

9. Growing Viruses Viruses must be grown in living cells.
Bacteriophages form plaques on a lawn of bacteria.
Figure 13.6

10. Growing Viruses
Animal viruses may be grown in living animals, or in embryonated eggs, or in tissue culture

11. Growing Viruses
Animal and plants viruses may be grown in cell culture.
Continuous cell lines may be maintained indefinitely.
Figure 13.8

12. 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)

13. 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

14. Lytic Lifecycle of a Bacteriophage I
Bacterial cell wall
Bacterial chromosome
Capsid
DNA
Capsid
Sheath
Tail fiber 1
Attachment: Phage attaches to host cell.
Tail
Base plate
Pin
Cell wall
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

15. 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

16. Lytic Life Cycle Overall

17. The Lytic and Lysogenic Cycles
Figure 13.12

18. 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