viruses

• Living

• Nonliving

• 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.

Virus Size

Figure 13.1

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.

Growth results.

• Plaques for bacteriophage.

• Cytopathic effects on cell culture.

Growing Viruses

• Viruses must be grown in living cells.– Bacteriophages

form plaques on a lawn of bacteria.

Figure 13.6

Growing Viruses

• Animal viruses may be grown in living animals or in embryonated eggs.

Figure 13.7

Growing Viruses• Animal and plants viruses may be grown in cell

culture.– Continuous cell lines may be maintained indefinitely.

Figure 13.8

Identification.

• Serological tests (Antibodies)

• RFLP and PCR

• (Discussion)

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

One-step Growth Curve

Figure 13.11

Lysogeny or Lytic?

The Lysogenic Cycle

Figure 13.12

Animal virus infection

• Attachment

• Penetration (endocytosis)

• Uncoating

• Biosynthesis

Attachment, Penetration, and Uncoating

Figure 13.14

Release of an enveloped virus by budding

Figure 13.20

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

Prions

Figure 13.21

PrPc

PrPSc

1 2 3 4

5 6 7 8

Endosome

Lysosome

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