© elsevier, 2011.principles of molecular virology introduction what is a virus? how are viruses are...

Principles of Molecular Virology © Elsevier, 2011.

IntroductionIntroduction

• What is a virus?

• How are viruses are different from other organisms?

• Are viruses alive?

• The history of virology how we think about viruses

• Techniques used to study viruses


What are viruses?What are viruses?

• Viruses are submicroscopic, obligate intracellular

parasites

• Most too small to be seen by optical microscopes

• Largest virus known (Mimivirus) = 400 nm diameter,

smallest bacteria (Mycoplasma) = 200 nm

• Largest virus genome (Mimivirus, 1.2 Mbp) twice as

big as smallest bacterial genome (Mycoplasma

genitalium, 0.58 Mbp)


How viruses are uniqueHow viruses are unique

• Virus particles are produced from the assembly of

preformed components, other biological agents

grow from an increase in the integrated sum of their

components and reproduce by division

• Virus particles (virions) do not grow or divide

• Viruses lack the genetic information that encodes

tools necessary for the generation of metabolic energy

or protein synthesis (ribosomes)


Are viruses alive?Are viruses alive?

• Viruses do not reproduce by division but are

assembled from preformed components

• Viruses cannot make their own energy or proteins

• A virus-infected cell is more like a factory than a

womb


The history of virologyThe history of virology

• First written record of virus infection ~ 3700 BC

- paralytic poliomyelitis

• Smallpox endemic in China by 1000 BC

• Edward Jenner, 14th May 1796 - smallpox vaccination

• Robert Koch and Louis Pasteur, 1880s

- germ theory of disease


The history of virologyThe history of virology

• 1892: Dimitri Iwanowski - "filterable particles”

- smaller than bacteria• 1898: Martinus Beijerinick - tobacco mosaic virus

- "soluble living germ"• 1898: Freidrich Loeffler and Paul Frosch

- foot-and-mouth disease in cattle• 1909: Karl Landsteiner and Erwin Popper

- poliomyelitis in humans• Frederick Twort (1915) and Felix d’Herelle (1917)

- bacteriophages


Living host systemsLiving host systems

• 1881: Louis Pasteur - rabies vaccine from rabbits

• 1900: Walter Reed - yellow fever caused by a virus

spread by mosquitoes

• Animal host systems still have their uses in virology:

–To produce viruses that cannot be effectively studied in vitro

(e.g. hepatitis B virus)

–To study the pathogenesis of virus infections (e.g. HIV and SIV)

–To test vaccine safety (e.g. oral poliovirus vaccine)


Living host systemsLiving host systems

• 1980's: transgenic animals which which carry the

genes of other organisms

• Transgenics are useful for understanding the

pathogenesis of viruses, prions


Cell Culture MethodsCell Culture Methods

1949: John Enders propagates poliovirus in human cells

1950s and 1960s: identification and isolation of many viruses

1952: Renato Dulbecco - plaque assay


Serological/Immunological MethodsSerological/Immunological Methods

• 1941: George Hirst - haemagglutination of red blood

cells by influenza virus• Improved detection methods for viruses:

Complement fixation tests

Radioimmunoassays

Immunofluorescence (direct detection of virus antigens in infected cells or tissue)

Enzyme-linked immunosorbent assays (ELISAs)

Radioimmune precipitation

Western blot assays


Serological/Immunological MethodsSerological/Immunological Methods


Monoclonal antibodiesMonoclonal antibodies


Ultrastructural StudiesUltrastructural Studies

Centrifugation of virus particles



• Spectroscopy - light-scattering properties

• X-ray diffraction

• Nuclear magnetic resonance (NMR)


Electron MicroscopyElectron Microscopy


Molecular BiologyMolecular Biology

Experimental techniques used to study the structure and function of biomolecules and their interactions

Focus on the virus genome:

• Molecular cloning

• Nucleotide sequencing

• Microarrays


Nucleic acid hybridizationNucleic acid hybridization

Blotting and probing for detection of DNA (Southern blot), RNA (Northern blot), proteins (Western blot)


Polymerase chain reaction (PCR)Polymerase chain reaction (PCR)


BioinformaticsBioinformatics


Further ReadingFurther Reading

Alberts, B., Bray, D., Hopkin,K., Johnson, A., Lewis, J., Raff, M., Roberts, K., Walter, P. and Johnson, A. (2009). Essential Cell Biology. 3rd Edition. Garland Science, New York. ISBN 0815341296

Forterre, P. (2010) Defining life: the virus viewpoint. Orig Life Evol Biosph. 40(2): 151-160

Hendrix, R.W. (2003). Bacteriophage genomics. Current Opinion in Microbiology, 6: 506–511

Lesk, A. Introduction to Bioinformatics. (2008) OUP Oxford; 3rd edition

Moreira, D., and López-García, P. (2009). Ten reasons to exclude viruses from the tree of life Nature Reviews Microbiology, 7 (4): 306-311

Primrose, S. and Twyman, R. Principles of Gene Manipulation and Genomics. (2006) Wiley-Blackwell 7th Edition

Raoult D, Forterre P. (2008) Redefining viruses: lessons from Mimivirus. Nat Rev Microbiol. 6 (4): 315-319

Sompayrac, L. How the Immune System Works. (2008) Wiley-Blackwell. 3rd edition

Villarreal L. (2004) Are viruses alive? Scientific American 291 (6): 100-105

© elsevier, 2011.principles of molecular virology introduction what is a virus? how are viruses are...

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