Bacteriophage

A bacteriophage ('eater of bacteria', from the Greek phagein, to eat) is simply a virus that infects bacteria; phages are abundant wherever bacteria are, including soil, sewage water, fruits, vegetables and milk. The T4 phage, which infects E. coli, is the structural model used to understand this whole group: it is tadpole-shaped, with a hexagonal head (built of about 2,000 identical protein subunits) that tightly packs in a double-stranded DNA molecule roughly 50 um long - remarkably, about 1,000 times longer than the phage particle itself. The head connects through a collar to a long helical tail with an inner tubular core, ending in a base plate arme …