If a colony of bacteria is infected with bacteriophages, the bacteria undergo chance collision and ultimately the phages attach to the bacterial cell wall through tail fibres. The DNA of the phage is injected into the host cell by dissolving the cell wall at the point of attachment, and the protein shell remains outside. The phage DNA takes up the control of the bacterial cell and replicates several times. The DNA and RNA of the bacterial cell are depolymerised and the nitrogen bases are utilised during the phage DNA replication. Similarly, the proteins of the bacterial cell are hydrolysed and the amino acids, thus formed, are used for building up of the protein shells of the virus. The newly-formed phage particles are released from the infected bacterial cells after lysis within 20min. to 1 hr. The new viruses infect other bacteria and a fresh cycle of virus replication is repeated.