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Viruses . Introduction . Viruses Infect. Humans Other vertebrates Invertebrates Plants Fungi Bacteria ....they infect all cellular life forms. Can they be found anywhere else?. Found in: soil, air and water (high conc in aqueous environments). Nature. Pathogenic Non pathogenic.
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Viruses Introduction
Viruses Infect.... • Humans • Other vertebrates • Invertebrates • Plants • Fungi • Bacteria • ....they infect all cellular life forms
Can they be found anywhere else? • Found in: • soil, • air and • water (high conc in aqueous environments).
Nature • Pathogenic • Non pathogenic
Is the study of viruses important? • Diseases • Infections: can spread rapidly in a susceptible population. • Cancer • Veterinary and plant virology?
Are they useful? • Phage typing of bacteria. Some groups of bacteria, such as some Salmonella species, are classified into strains on the basis of the spectrum of phagesto which they are susceptible. • Sources of enzymes. A number of enzymes used in molecular biology are virus enzymes. • Pesticides. Some insect pests are controlled with baculovirusesand myxoma virus has been used to control rabbits. • Anti-bacterial agents. In the mid-20th century phageswere used to treat some bacterial infections of humans. Interest waned with the discovery of
Anti-cancer agents. Genetically modified strains of viruses, such as herpes simplex virus and vaccinia virus, are being investigated for treatment of cancers. • Gene vectors for protein production. Viruses such as certain baculoviruses and adenoviruses are used as vectors to take genes into animal cells growing in culture. • Gene vectors for treatment of genetic diseases.
Discoveries thanks to viruses • A famous experiment carried by Alfred Hershey and Martha Chase, and published in 1952, used phage T2 and E. coli to provide strong evidence that genes are composed of DNA. • The first enhancers to be characterized were in genes of simian virus 40 (SV40). • The first transcription factor to be characterized was the transplantation (T) antigen of SV40. • The first nuclear localization signal of a protein was identified in the T antigen of SV40. • Intronswere discovered during studies of adenovirus transcription.
Basic Properties • Size • small • The units in which virions are normally measured are nanometres (1 nm = 10−9 m). • 20-400nm • Amongst the smallest are parvoviruses, with diameters about 20 nm, while the microbe-mimicking virus (mimivirus), isolated from an amoeba, is amongst the largest.
Virions are not cells. They do not contain organelles. • Except for the virions of the arenaviruses, which contain cell ribosomes that were packaged when the virionswere assembled.
Viruses have genes • The virion contains the genome of the virus. • Whereas the genomes of cells are composed of double stranded DNA, there are four possibilities for a virus genome: • double-stranded DNA • single-stranded DNA • double-stranded RNA • single-stranded RNA.
The genome is enclosed in a protein coat known as a capsid. • The genome plus the capsid, plus other components in many cases, constitute the virion. • The functions of the virion are to protect the genome and to deliver it into a cell in which it can replicate.
