viruses

1
viruses
2

• Living
• Nonliving

3

• Contain a single type of nucleic acid (DNA or
  RNA), protein coat, sometimes an envelope.
• Are obligatory intracellular parasites. Multiply
  by using host cells synthesizing machinery to
  cause the production of specialized elements that
  can transfer the nucleic acid to other cells.

4

• Multiply inside living cells by using the
  synthesizing machinery of the cell.
• Why does this make targeting viruses difficult?

5
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 cells surface and the
  availability of host cellular factors.

6
Virus Size
Figure 13.1
7
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

8
Viral Taxonomy

• Herpesviridae
• Herpesvirus
• Human herpes virus 1, HHV 2, HHV 3
• Flue H1N1

• Retroviridae
• Lentivirus
• Human Immunodeficiency Virus 1, HIV 2

9
Isolation, growth and identification

• Must be grown on living cells.
• Easiest to grow are bacteriophage, because
  bacteria are easy to grow.

10
Growth results.

• Plaques for bacteriophage.
• Cytopathic effects on cell culture.

11
Growing Viruses

• Viruses must be grown in living cells.
• Bacteriophages form plaques on a lawn of bacteria.

Figure 13.6
12
Growing Viruses

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

Figure 13.7
13
Growing Viruses

• Animal and plants viruses may be grown in cell
  culture.
• Continuous cell lines may be maintained
  indefinitely.

Figure 13.8
14
Identification.

• Serological tests (Antibodies)
• RFLP and PCR
• (Discussion)

15
Typical viral infection

• Attachment
• Penetration
• Biosynthesis
• Maturation
• Release
• Burst size and burst time

16
Bacterial cell wall
Bacterial chromosome
Capsid
DNA
Capsid
Sheath
Tail fiber
Tail
1
AttachmentPhage attaches to host cell.
Base plate
Pin
Cell wall
Plasma membrane
2
PenetrationPhage pnetrates host cell and
injects its DNA.
Sheath contracted
Tail core
3
Merozoites released into bloodsteam from liver
may infect new red blood cells
Figure 13.10.1
17
Tail
DNA
4
MaturationViral components are assembled into
virions.
Capsid
5
ReleaseHost cell lyses and new virions are
released.
Tail fibers
Figure 13.10.2
18
One-step Growth Curve
Figure 13.11
19
Lysogeny or Lytic?
20
The Lysogenic Cycle
Figure 13.12
21
Animal virus infection

• Attachment
• Penetration (endocytosis)
• Uncoating
• Biosynthesis

22
Attachment, Penetration, and Uncoating
Figure 13.14
23
Release of an enveloped virus by budding
Figure 13.20
24
Multiplication of DNA Virus
1
Papovavirus
Virion attaches to host cell
7
Virions are released
Host cell
DNA
Capsid
2
Virion penetrates cell and its DNA is uncoated
DNA
Cytoplasm
6
Virions mature
Capsid proteins
mRNA
5
Late translation capsid proteins are synthesized
3
Early transcription and translation enzymes are
synthesized
4
Late transcription DNA is replicated
Figure 13.15
25
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?

26

• 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)

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Prions

• Infectious proteins
• Inherited and transmissible by ingestion,
  transplant, surgical instruments
• Spongiform encephalopathies Sheep scrapie,
  Creutzfeldt-Jakob disease, Gerstmann-Sträussler-Sc
  heinker syndrome, fatal familial insomnia, mad
  cow disease
• PrPC, normal cellular prion protein, on cell
  surface
• PrPSc, scrapie protein, accumulate in brain cells
  forming plaques

28
Prions
PrPSc
PrPc
2
3
4
1
Lysosome
Endosome
5
6
7
8
Figure 13.21
29
Topics on the flue

• http//content.nejm.org/cgi/content/full/NEJMe0903
  995
• NEJM N1H1 site http//h1n1.nejm.org/
• An Old presentation http//www.strongnet.org/17152
  0529114210850/lib/171520529114210850/Influenza_pre
  sentation.pdf