Notes on VIruses and Disease module at King's College London, but is very simple to understand and can be used for other courses. Notes are in detail and laid out in a clear order of lectures.
Why study viruses?
1. Viruses are everywhere
2. Viruses cause human disease
3. Viruses infect all living things - affect society
4. Viruses can cross species boundaries - zoonotic (Ebola found in bats)
5. Endogenous Viruses make up 5-8% of our DNA
6. Studying biology
8.) Gene therapy (Vectors)
Rous sarcoma virus experiment:
RSV (Rous Sarcoma Virus) was discovered in 1911 by Rous by injecting cell free extract of
chicken tumor into healthy chickens.
The extract was found to induce oncogenesis (induced sarcoma development)
Thus, RSV became known as the first oncogenic retrovirus.
History of Virology:
Ancient World (3700 B) - Egyptian mummy with poliomyletis, first recorded evidence of viral
infections.
Iwanowski (1892) – showed that extracts from tobacco plant can transmit disease to other
plants. Hypothesised that filterable agent in extract was bacterium. Later discovered to be
Tobacco Mosaic Virus.
Beijerinck (1898) – showed that filterable agent in tobacco plant extract could not be
bacterium because it could not be cultured. He named the new pathogen ‘ virus.’
Frosch and Loeffler – Discovered that infectious filterable agents comprised small particles
Stanley (1935)- Crystallised Tobacco Mosaic Virus (TMV). Showed that viruses consist of
protein and genetic material.
Characteristics of Viruses
Definition: Infective agent that typically consists of a nucleic acid molecule in a protein coat,
too small to be seen by light microscopy and is able to multiply within a living host.
Size - 20nm to 200nm (<300nm)
Obligate – replication only occurs in living cells
Contain DNA or RNA (nucleic acid)
Hijack host machinery
Produces virion progeny
Have mechanisms to counteract host response
The Viral protein coat
Capsid: protein shell surrounding the viral genome
Nucleocapsid: nucleic acid - protein complex
The capsid is composed of repeated units of different
polypeptides.
Subunit: single folded polypeptide chain (e.g VP1,
VP2, VP3 see diagram)
Structural unit (asymmetric unit): unit from which
capsids or nucleocapsids are built (see diagram).
Viral nucleocapsids are either helical or icosahedral
Example of helical (Vesicular stomatitis virus)
Example of icosahedral (Papilloma virus, Polio virus)
*Some viruses have an additional phospholipid envelope layer
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