11 Nov

Bacteriophage Life Cycle

The bacteriophage life cycle involves recognizing the host cell, replicating itself and ultimately releasing the newly formed virion or single phage unit.  A bacteriophage consists of a capsid (nucleic acid and protein) that is attached to a protein sheath that is a hollow tube in the center.  The sheath is on top of a base plate to which tail fibers are connected.  This structure allows the phage to insert its DNA into the host cell.  The phage recognizes the appropriate host cell by way of its tail fibers.  The tail fibers recognize chemical groups on the surface of the host cell.  Phages cannot bind to host cells that do not have the appropriate chemical groups.  A lysozyme associated with the tail fiber breaks down the cell wall and the sheath inserts the DNA into the host cell.  The phage also inserts a nuclease which destroys the host cell DNA.  The phage leaves the host cell’s metabolic machinery intact so that its DNA can be replicated.  The components of the virus are constructed and come together to form the complete phage.  One phage can replicate into 200 phage particles within the host cell.  The host cell then bursts and releases the phage particles so that they can infect other cells.