What are viruses about
What about Viruses:
Apparently all viruses are parasitic, living inside the cells of their hosts. Viruses combine characteristics of the living and non-living. Outside their hosts viruses seem inert and can survive indefinitely in a desiccated crystalline state. Once inside a suitable host cells the virus becomes able to reproduce itself; the virus takes over the cell’s metabolism for its own uses, i.e. to reproduce more virus. Eventually the cell dies and bursts, liberating the reproduced viruses.
Viruses are ultra-microscopic; all are able to pass through filters which retain bacteria. Although their presence was demonstrated in 1892, viruses could not be seen until the development of the electron microscope. The largest viruses measure 0.00035 mm, the smallest 0.00001 mm. each virus essentially consists of the large chemical molecules that are elsewhere associated with the nuclei of plant and animal cells, i.e. nucleo- proteins.
The shapes of viruses vary from spheres, cubes and rods to flat plates and spheres with a tail. In many, the protein components are arranged in complex geometric patterns.
In some viruses the protein coat is surrounded by a further external covering.
Viruses are generally named after the diseases they cause, though in some cases the symptoms of the virus attack are insufficient to warrant the term disease; for example, some plant viruses cause the production of variegated foliage only.
Economically important virus diseases of plants include the leaf mosaics of tobacco, potato and tomato. They are transmitted by insects such as greenfly. In animals, viruses cause poliomyelitis, influenza, the common cold, chickenpox, measles, rabies (in man), distemper (in dogs), myxomatosis (in rabbits), foot-and-mouth (in cattle), fowl pest and swine fever. They also seem to cause certain types of cancer.
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Mammals protect themselves against viruses with the same methods that are used against bacteria. However viruses are not affected by anti-biotics.