Lambda Phage Infect Bacteria Differently
(Answer Sheet)
The lambda bacteriophage also infects Escherichia coli bacteria, but
does not cause lysis of the host cell. In the process called lysogeny , the
virus appears dormant, and this interruption of replication can last a long
time.
Figure 3: Lysogenic Cycle
The bacterial DNA is usually
a closed circle. When Lambda
phage DNA penetrates the
bacterium, it then integrates
into the bacterial DNA. From this
point on, the virus appears to be
in a dormant state. The bacterium
will grow and divide normally,
copying the viral DNA along with
its own. Over a longer period of
time, the result will be many
bacteria all carrying copies of
the viral DNA.
The trigger that ends
lysogeny and activates the virus
is induction . Excision
of the
viral DNA will then occur –
becoming a free loop once again. The lytic
phages are produced.
cycle then resumes and many
Occasionally the viral DNA will take along a piece of the
bacterial chromosome when it is excised. All of the phage then produced will
have copies of this DNA inside them. When they infect another bacterium they
give it new genes. This virus-mediated
transfer of DNA between bacteria is called transduction. Viruses can thus
help create genetic variation among their host cells.
Host chromosome
Phage lands
on bacterium
Bacterial cell
Phage injects its
DNA into cell
Injection of
DNA
Phage DNA replicates and
Synthesis of
viral proteins
Replication of
viral DNA and
viral construction
Cell lysis releases
large numbers of
viruses
Integration of
viral DNA into
bacterial DNA
Cell division
Lysogenic
Pathway
Lytic
Pathway
new phage proteins
are made
Phage particles
assemble
Cell bursts, releasing
new phage viruses