Viruses can proliferate in bacteria cells, animal cells, and plant cells. To explain the virus proliferation, a sample virus attacking bacteria viruses (bacteriophage) is usually used. For example the virus which attacks the bacteria of Escherichia coli.
The proliferation of bacteriophage forms cycles. The cycles of bacteriophage are divided into two, those are lytic and lysogenic cycles.
1. Lytic Cycle of Bacteriophage
In this cycle, the bacteria cells fall to pieces (lysis) so it is called lytic cycle. Their reproduction startes by attacchment of viruses on the bacteria. Virus enzyme dissolves the wall of bacteria cells, so it formes a hole and through the hole, viruses anter their DNA into the bacteria. Later the DNA of virus takes over the duty of bacteria DNA by destroying the DNA of bacteria. Afterwards in the body of bacteria, DNA, shield protein, and other parts of virus body are synthesized (one bacteria is cell enough to form 300 new viruses). After new viruses are formed, the wall of bacteria cell falls to pieces (lysis), the newly formed viruses get out and infect the other bacteria.
To better understand the lytic cycle of bacteriophage, study the figure below.
2. Lysogenic Cycle of Bacteriophage
In this cycle, the DNA of viruses only attaches itself on the DNA of bacteria. The DNA of viruses sticking on the DNA of bacteria is called prophage. Lysogenic cycle occurs if bacteria have immunity so the virus becomes not invirulent.
The DNA of viruses is entered into bacteria cells but formation of the parts of virus body does not happen. If the bacteria reproduce divide than selves the prophage also divides so that every bacterium resulting from the division contains prophage. If the bacteria immunity system is lost, the prophage will become virulent and the bacteria will fall to pieces (lysis) because new viruses (prophage) are formed. Consefuently, lysogenic cycle can change into lysis cycle if the surrounding changes and the immunity of bacteria decreases.
To better understand the lysogenic cycle of bacteriophage, study the figure below.
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