viruses
DESCRIPTION
viruses. Living Nonliving. Contain a single type of nucleic acid (DNA or RNA), protein coat, sometimes an envelope. - PowerPoint PPT PresentationTRANSCRIPT
• Contain a single type of nucleic acid (DNA or RNA), protein coat, sometimes an envelope.
• Are obligatory intracellular parasites. Multiply by using host cell’s synthesizing machinery to cause the production of specialized elements that can transfer the nucleic acid to other cells.
• Multiply inside living cells by using the synthesizing machinery of the cell.
• Why does this make targeting viruses difficult?
Host Range
• The spectrum of host cells in which a virus can multiply.
• Mot viruses infect only specific types of cells in one host species.
• The host is determined by the specific attachment site on the host cell’s surface and the availability of host cellular factors.
Taxonomy of viruses
• Currently based on type of nucleic acid, strategy for replication and morphology.
• Virus family names end in –viridae; genus names end in –virus
• A viral species is a group of viruses sharing the same genetic information and ecological niche
Viral Taxonomy
• Herpesviridae
• Herpesvirus
• Human herpes virus 1, HHV 2, HHV 3
• Flue H1N1
• Retroviridae
• Lentivirus
• Human Immunodeficiency Virus 1, HIV 2
Isolation, growth and identification
• Must be grown on living cells.
• Easiest to grow are bacteriophage, because bacteria are easy to grow.
Growing Viruses
• Viruses must be grown in living cells.– Bacteriophages
form plaques on a lawn of bacteria.
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
Typical viral infection
• Attachment
• Penetration
• Biosynthesis
• Maturation
• Release
• Burst size and burst time
Figure 13.10.1
Attachment:Phage attaches to host cell.
Penetration:Phage pnetrates host cell and injects its DNA.
Merozoites released into bloodsteam from liver may infect new red blood cells
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
Figure 13.10.2
4 Maturation:Viral components are assembled into virions.
Tail
5 Release:Host cell lyses and new virions are released.
DNA
Capsid
Tail fibers
Multiplication of DNA Virus
Figure 13.15
Virion attaches to host cell
Virion penetrates cell and its DNA is uncoated
Early transcription and translation; enzymes are synthesized
1
2
3
DNA
Late transcription; DNA is replicated
4
Late translation; capsid proteins are synthesized
5
Virions mature6
Capsid
Papovavirus
Host cell
DNA
Cytoplasm
Virions are released7
Capsid proteins
mRNA
Viruses and Cancer.
• Viruses incorporated in to the host genome can cause mistakes and errors resulting in unchecked growth of the cell.
• It this accidental or are these sites targeted?
• Latent Viral Infections– Virus remains in asymptomatic host cell for long
periods• Cold sores, shingles
• Persistent Viral Infections– Disease processes occurs over a long period,
generally fatal• Subacute sclerosing panencephalitis (measles virus)
• Infectious proteins
• Inherited and transmissible by ingestion, transplant, & surgical instruments
• Spongiform encephalopathies: Sheep scrapie, Creutzfeldt-Jakob disease, Gerstmann-Sträussler-Scheinker syndrome, fatal familial insomnia, mad cow disease
• PrPC, normal cellular prion protein, on cell surface
• PrPSc, scrapie protein, accumulate in brain cells forming plaques
Prions
Topics on the flue
• http://content.nejm.org/cgi/content/full/NEJMe0903995
• NEJM N1H1 site http://h1n1.nejm.org/
• An Old presentation http://www.strongnet.org/171520529114210850/lib/171520529114210850/Influenza_presentation.pdf