Phage

A Phage or Bacteriophage (from the Greek word phagein meaning "to eat") is a class of virus that will infect bacterial hosts, they are also used as model organisms for the study of the molecular biology and replication of viruses. A key example is the T4 phage that will infect an E.coli host cell. T4 phages are made up a a protein head that contains the genetic information of the virus, along with a tail and tail fibres that permit the injection of genetic material into the host cell, these structures are made of protein  .