T4 phage

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Phage T4 is a Bacteriophage which infects Escherichia coli.

It is known as a Caudovirales under the Baltimore Classification system of viruses meaning it is a tailed bacteriophage with double stranded DNA. It infects by the lytic lifecycle which means it hijacks cell machinery so host cell is killed.

Infection starts by creating a hole in the lipopolysaccaride and peptodoglycan of the bacteria by injecting a lysozyme complex. After injection, the cells DNA is hydrolysed so the E.coli now contains the phage DNA but the T4 phage is using the cells machinery to produce lysozyme which digests the cell wall causing it to burst open[1].

The dsDNA is found in the isosachedral head of the phage which then leads onto a tail made of a helical sheath with tail fibres to help with the attachment and injection into the host cell[2].


  1. Michael Madigan, John Martinko, David Stahl, David Clark. (2012) Brock Biology of Microorganisms, Thirteenth Edition, San Francisco: Pearson. 267-268
  2. Jeremy M. Berg, John L. Tymokzo, Lubert Stryer, (2007), Biochemistry, 6th edition, New York, W. H. Freeman and Company.
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