Lect 1 history and terminology DinmanDocument Transcript
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Impact: It is important to study
•Many important infectious diseases
that afflict humankind are caused
by viruses. These can be fatal,
uncomfortable and very contagious,
cause congenital defects, or
•Viruses can affect the food supply:
crop plants and food animals.
•The relatively simple nature of
viruses makes them useful as model
systems for many of the basic
problems in biology.
Virology, lect. 1.
Viruses in antiquity:
Viruses in antiquity:
Ramses V had smallpox
Tulip mosaic virus: Varigated
tulips first described in 1576
Smallpox: first described in India,
Viruses are small!
Filter systems used to
Tobacco mosaic virus:
ultrafiltrate by Mayer
The pace of early
discovery of new
and animal viruses:
the three general
areas of virology
Advances from plant
The ability to isolate large amounts
of viruses from plants permitted
extensive chemical and physical
•The first demonstration that
viruses consisted of proteins
and nucleic acids.
•The crystallization of TMV by
Stanley (1935) was a paradigm
shift in that it demonstrated
that agents able to reproduce in
living cells could also behave like
· Initial focus on the hypothesis of bacteriophage
as antibacterial therapies.
· Although this proved to be untenable, this work
set the technological foundation for molecular
biology as we know it. Examples include:
· Discovery that nucleic acids are the molecules of
genetic inheritance (Hershey & Chase 1952, also
credit Oswald, MacLeod and McCarthy, 1944),
· The first model systems for DNA replication
· Control of gene expression and recombination
· Discovery of mRNA
· Elucidation of the factors that control initiation
and termination of both transcription and
translation of genetic information,
· Discovery of restriction endonucleases.
·Pathogenesis of viral infections
·The need to study animal viruses
spurred the development of
techniques for growing animal cells
in vitro. -HeLa cells
·Animal virus systems also played a
large role in the development of
Animal virus research
Understanding of cellular functions e.g.:
•DNA replication and repair (SV40),
•RNA splicing (adenoviruses),
•Translation (picornaviruses, poli),
•Gene expression (retroviruses),
•Cancer and malignancy.
•Oncogenes originally discovered in
•Therapeutics: Vectors to introduce foreign
genes into bacteria (insulin) or animals (gene
therapy and vaccine development.
•Commonly used vectors are based on
poxviruses, retroviruses, adenoviruses
•A particular vector may be able to
home in on particular cell types (ex.
Adenovirus-respiratory tract cells,
retrovirus-mmune system cells)
•others may be more general.
The “New” Molecular
Biology is founded on
The Origin of Viruses
Three possible origins:
1. Products of regressive
evolution from free living
cells. Best candidate are
2. Derived from cellular
genetic material that has
acquired the capacity to
exist and function
3. Leftovers from the pre-
biotic RNA world.
Definition of a Virus.
• A genetic element containing either
RNA or DNA that is able to alternate
between intra- and extracellular
states, the latter being the infectious
• Viruses are obligate intracellular
parasites. They are absolutely
dependent on the host cells’ synthetic
and energy-yielding apparatus.
• Viruses consist of a nucleic acid
genome that is protected by a protein
component (typically surrounded by a
protein shell called a nucleocapsid).
Frequently, there is a second outer
shell composed of lipids and proteins.
• Virion- Morphologically complete
(mature) infectious virus particle.
• Pathogen- Biological disease agent.
• Bacteriophage- Viruses that infect
bacteria. Phage is Greek for
eating, since bacteriophage
produced hole on lawns of bacteria.
• Virulence- the ability of an
infectious agent to produce
disease. Many viruses are virulent
sometimes and asymtomatic at
• A virus is an infectious agent and
obligate intracellular parasite.
• Virus infectious cycle includes a phase
in which the agent consists of a virion.
• The virion consists of RNA or DNA
coated with one or more proteins
(capsid structure) which is sometimes
coated with a membrane containing
lipid and glycoproteins.
• A virus can initiate another infection
when transferred to a suitable host.
• A virus carries genetic information in
the form of RNA or DNA. This
genomic nucleic acid carries
information which redirects the
genetic and metabolic apparatus of the
1. Cell attachment – binding
to a cell surface
2. Entry via receptor—
3. Release of genome into
cytoplasm via membrane
4. Transcription of viral
mRNAs and of new viral
genomes (RNA viruses)
5. Viral protein synthesis
and assembly of provirus.
6. Maturation of viral
7. Release of virus from
8. Evasion of host defense
and transmission to new
The common tasks faced by
(almost) all viruses.
Effects on Host Cells
• Inhibition of Host
• Changes in Regulation of Host
• Appearance of New Antigenic
Determinants on the Cell
• Cell Fusion.
a) HIV-1 infected T-