Download viruses

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
Bacterial
cell wall
Bacterial
chromosome
Capsid
DNA
Capsid
Sheath
Tail fiber
1 Attachment:
Phage attaches
to host cell.
Base plate
Pin
Cell wall
Tail
Plasma membrane
2 Penetration:
Phage 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
Tail
DNA
4 Maturation:
Viral components
are assembled into
virions.
Capsid
5 Release:
Host cell lyses and
new virions are
released.
Tail fibers
Figure 13.10.2
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
Papovavirus
1 Virion attaches to host cell
7 Virions are released
Host cell
DNA
Capsid
DNA
2 Virion penetrates
cell and its DNA is
uncoated
Cytoplasm
6 Virions mature
Capsid proteins
mRNA
5 Late translation;
capsid proteins
are synthesized
4 Late transcription;
DNA is replicated
3 Early transcription and
translation; enzymes are
synthesized
Figure 13.15
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)
Prions
• 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
PrPSc
PrPc
1
2
3
4
Lysosome
Endosome
5
6
7
8
Figure 13.21
Topics on the flue
• http://content.nejm.org/cgi/content/full/NEJ
Me0903995
• NEJM N1H1 site http://h1n1.nejm.org/
• An Old presentation
http://www.strongnet.org/17152052911421
0850/lib/171520529114210850/Influenza_
presentation.pdf