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

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

SheathTail fiberBase platePinCell 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.