LYTIC AND LYSOGENIC CYCLES - PHAGE MULTIPLICATION CYCLE
A. Definition - Lytic or virulent phages are phages which can only multiply on bacteria and kill
the cell by lysis at the end of the life cycle.
Lytic or Virulent Phages
a. Eclipse period - During the eclipse phase, no infectious phage particles can be found either
inside or outside the bacterial cell. The phage nucleic acid takes over the host biosynthetic
machinery and phage specified m-RNA's and proteins are made. There is an orderly expression
of phage directed macromolecular synthesis, just as one sees in animal virus infections. Early
m-RNA's code for early proteins which are needed for phage DNA synthesis and for shutting off
host DNA, RNA and protein biosynthesis. In some cases the early proteins actually degrade the
host chromosome. After phage DNA is made late m-RNA's and late proteins are made. The late
