Viruses which infect bacterial cells are known as bacteriophage or bacteria eaters. They contain DNA as genetic material. There are many varieties of bacteriophages. Usually, each kind of bacteriophage will attack only one species or only one strain of bacteria.
fig:structure of bacteriophage
The shape and size of bacteriophage may vary from species to species. Some are spherical, comma- shaped while some are tadpole-shaped with a polyhedral head, a short neck, collar and straight tail. The head is bipyramidal hexagonal in shape. The contents of the head are enclosed by a capsid which is about 35ºA thick. The head enclosed a double stranded greatly folded DNA which contains more than 75 genes. The tail is a hollow structure that is enclosed by a spring-like a contractile sheath.
Chemically viruses are nucleoprotein entities, which are composed of nucleic acid and proteins. Nucleic acid forms the central core and is surrounded by a protein coat. The capsid is composed of a number of subunits called capsomeres. The capsomeres are closely packed and are arranged in the helical or polyhedral in shapes. The nucleic acid occupies about 1-4 % of the whole amount of the virus. It is tightly fitting by a protein sheath. The nucleic acid is of either DNA or RNA.
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