Coloured transmission electron micrograph (TEM) of a section through an Escherichia coli bacterium infected with T4 bacteriophage (phage) viruses (red). One T4 phage is on the surface of the bacterium (top right). The phage consists of a large DNA-containing head and a tail composed of a central sheath with several fibres. The fibres attach to the host cell surface and the phage DNA (deoxyribonucleic acid) is injected into the cell through the sheath. The phage DNA hijacks the bacterium's own cellular machinery, forcing it to produce more copies of the bacteriophage (progeny, in cell). When a sufficient number have been produced, the phages burst out of the cell, killing it. Magnification: x60,000 when printed at 15cm wide.