VIRUS

1. The development of virology2. TMV virus3. Lambda phage4. HIV

The development of virology

Start of 20th centaury

Infectious diseases attributed to parasitic fungi and bacteria

The development of virology

1892

Tobacco mosaic disease induced in healthy plants by rubbing their leaves with juices from infected plants after filtering through bacterial filters

The development of virology

1892

Foot and mouth disease shown to be passed on in bacterial filtered fluids from infected animals

The development of virology

1898

Recognised that there must be a “new” type of infectious agent – the term “virus” introduced

The development of virology

Early 1900’s

Established that viruses propagate only in living cells, i.e. obligate intracellular parasitesViruses capable of destroying Staphylococci identified

The development of virology

1917

Viruses capable of destroying dysentery bacilli identifiedBacterial viruses now called bacteriophages.

The development of virology

1930’s

Established that viruses are particulate, virus particles called virions.

The development of virology

1935

Tobacco mosaic virus (TMV) purified

The development of virology

1936

Established that TMV is a nucleo-protein capable of crystallization.This suggests a simplicity and regularity to their structure

The development of virology

Subsequent studies

Possible to separate the protein and nucleic acid of viruses and demonstrate that the nucleic acid component alone is capable of initiating infection.

The development of virology

Structural and chemical composition of viruses

Understanding virus structure has been dependent upon the development of such methods as chromatography, electrophoresis, density gradient centrifugation, electron microscopy and X-ray diffraction

The development of virology

Structural and chemical composition of viruses

Simplest viruses, e.g. TMV, consist of only protein and nucleic acidViruses only ever have one type of nucleic acid

The development of virology

Three basic virus groups

RNA virus e.g. Tobacco mosaic virus, TMVDNA virus e.g. bacteriophageRNA retrovirus e.g. HIV

The development of virology

Most of the proteins in a virus occur as a coat, called a caspid, surrounding the nucleic acidThe protein protects the nucleic acid from hostile environmental conditionsThe protein also aids the penetration of the host cell.The outer coat (the caspid) is made out of sub-units called capsomeres, arranged in a helical pattern

Tobacco Mosaic Virus (TMV)Rod shaped 300nm long, diameter 15nm94% protein,6% RNA

Tobacco Mosaic Virus (TMV)Attacks tomato, blackcurrant, potato, orchid and tobacco.Causes irregular mottled patches to appear on leaves of plants which indicate areas where cells and tissues have been killed by the virus

Tobacco Mosaic Virus (TMV)Carried on seed coats, by grasshoppers and by other mechanical means

Tobacco Mosaic Virus (TMV)Control measures include

Avoidance of growing susceptible crops in soil known to be contaminatedSterilisation of soil used for seed bedsHygienic handling of crops by workersUse resistant varieties of crops

The lambda phageAlso known as:

T4-phage

The lambda phageAn example of a bacteriophage (A virus that uses bacterium as its host)Invades the bacterium Escherichia coli

The lambda phageCan destroy the host cell or insert its DNA into the bacterial chromosome and remain dormant for several generations

The lambda phageConsists of a head, containing a double stranded DNA molecule wrapped around a core of protein surrounded by a polyhedral capsule and a helical tail.