Life Cycle of Bacteriophage

Life Cycle of Bacteriophage. Bacteriophage: Bacteria eating virus is called bacteriophage. Life Cycles: There are 2 types of lifecycles that occur in the bacteriophage: 1) Lytic Cycle 2) Lysogenic Cycle 1) Lytic Cycle: In lytic cycle, virus that is the bacteriophage causes lysis of the host cell. It is virulent phage. 2) Lysogenic Cycle: In lysogenic cycle, the bacteriophage does not cause lysis of host’s cell. It is avirulent phage. Lytic Cycle. Landing, Penetration and Attachment
To infect a cell, a virus must first enter the cell through the plasma membrane and (if present) the cell wall. Viruses do so by either attaching to a receptor on the cell’s surface or by simple mechanical force using tail fibers. Attachment is done with the help of receptors. Control The virus then releases its genetic material (either single- or double-stranded RNA or DNA) into the cell. In doing this, the cell is infected and can also be targeted by the immune system. This relation is called master-slave relation.
Biosynthesis The virus’ nucleic acid uses the host cell’s machinery to make large amounts of viral components. For DNA viruses, the DNA transcribes itself into messenger RNA (mRNA) molecules which are afterwards used to control the cell’s ribosomes. The first polypeptides that are translated destroy the host’s DNA. In retroviruses , an enzyme called reverse transcriptase translates the viral RNA into DNA, which is then translated again into RNA. Assembly New viruses are formed by the assembly of the different parts of the virus.

After approximately 25 minutes, 200 new viruses are formed. Release Bacterial cell burst and the newly formed viruses are released from the host cell. Now, they are ready to attack new bacteria. Lysogenic Cycle. Landing The first step of lysogenic cycle is landing of the virus on the host’s cell. This is done by tail fibers. Attachment It is done with the help of receptors present on the surface of the bacterial cell wall. Penetration For the penetration the tail fibers of the bacteriophage secrete special enzymes for the lysis of bacterial cell wall called, “lysozyme. Then by the contraction of tail fibers and sheath viral DNA is injected into bacterial cell. Incorporation Viral DNA after penetration becomes incorporated (inserted) into bacterial DNA. This state is called prophage and this relation is called “host-guest” relation. Bacterial Division Bacteria divides and the daughter bacterial cell receives the viral DNA. These bacterial cells having viral DNA are resistant to viral attack. Induction During lysogenic cycle when viral DNA detaches from bacterial DNA, and take control over bacterial DNA. Now, lytic cycle begins.