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 Herpesvirus Human herpes virus 1, HHV 2, HHV 3 Retroviridae Lentivirus 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. 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 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