(1) The viruses which attack bacteria are called bacteriophages .They were discovered by Twort (1915).
(2) Fellx .d. Herelle(1917) coined the term Bacteriophage.
(3) Bacteriophage are tadpole -shaped with a large head and a tall .
(4) The head is hexagonal and is capped by hexagonal pyramid , measure about 65 x 95 nm.
(5) The head is formed with several capsomers ,each of which is a single protein .
(6) The head protein forms a semipermeable membrane enclosing the folded double stranded DNA which is 1000 times longer than the phage .
(7) The tail is composed of several parts present around central core .
(8) The tail core is 95 nm long 8 nm in diameter .It is surrounded by tail sheath composed of 144 sub - units which are arranged in 24 rings of 6 each .
(9) The head and tail are joined by collar whose function is not known .
(10) At the tip of the tail , hexagonal tail plate is present with six tail pins and tail fibres .
(11) The tail fibres help in attachment of the phage on to the host cell .
