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Comparative studies of natural groups of organisms
termed as lytic phase from the word lysis with the bacterial DNA while in a lytic
meaning ‘digest’. The host cell lysis and cycle, the viral DNA and the host DNA
release of phages mark the culmination replicate separately within the host cell,
of the lytic phase (Figure 3.3). The newly resulting in many copies of the virus being
produced phages are capable of infecting a produced very quickly. Also, the lysogenic
new bacteria and the cycle starts over again cycle does not lyse the host cell straight
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as lysogenic cycle with or without a break away, while in the lytic cycle, the host cell
or dormant stage. is lysed or destroyed.
The lysogenic and lytic cycles can be Phages that replicate using both lytic and
distinguished due to the fact that, in
lysogenic cycles, the spread of the viral lysogenic cycles are called temperate phages
DNA occurs through the usual bacterial while phages that replicate through the lytic
reproduction as their DNA has incorporated cycle are called virulent phages.
Bacterial
Phage cell DNA
Bacterial cell Phage particle approaches a bacterial cell
Phage attaches to a bacterial cell wall. DNA
is injected into bacterial cell and protein
‘ghost’ is left outside
Empty protein coat
The DNA of phage becomes incorporated
into bacterial DNA
The bacterial cells divides to
produce two cells whose DNA still
incorporates the DNA of the phage.
Phage DNA inside the bacterial cell multiplies
using bacterial nucleic acid and other substances
absorbed by the bacterium
Phage DNA induces formation of protein
coat. Eventually, bacterial cell bursts (lysis),
releasing about 200 exact copies of the
original phage
Figure 3.3: The life-cycle of a lytic (virulent) phage
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