Bacteriophage
A bacteriophage or just phage is a virus that infects bacteria. The T4 phage is an example of a bacteriophage. The head and tail of the bacteriophage ae constructed from proteins. The head contains the viral DNA and the tail is a hollow tube used to inject a host cell during infection, though not all phages have a tail. The head can icosahedral (20 sided) or filamentous, and the tail can be coated with a contratile sheath or in the case of the T phage have a base plate attached[1]
Three basic bacteriophage types can be distinguished from their capsid structures. The first of these have icosahedral capsids, in which individual protein subunits (known as protomers) are arranged into a 20-faced geometric structure that surrounds the nucleic acid. Examples of icosahedral bacteriophages are MS2, which infects Escherichia coli, and PM2 which infects pseudomonas aeruginosa. The second type have filamentous capsids, in which the protomers are arranged in a helix, producing a rod shaped structure. The E.coli bacteriophage M13 is an example. The head-and-tail bacteriophages combine the features of the other two types. Their capsid is made up of an icosahedral head, containing the nucleic acid, and a filamentous tail, which facilitates entry of the nucleic acid into the host cell. They may also have have other structures, such as the 'legs' possessed by the E.coli bacteriophage T4. [2]
==== References ====
- ↑ http://pathmicro.med.sc.edu/mayer/phage.htm
- ↑ Brown, Terry. (2012). Chapter 13: Inheritance of Genes During Virus Infection Cycles. In: Clayton, J. and Owen, E. Introduction to Genetics: A Molecular Approach. New York, USA: Garland Science, Taylor & Francis Group LLC. p255.