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Conjugation
As
we saw in the
page on Binary
Fission,
prokaryotes have
a simple and
accurate way to
reproduce
themselves.
However,
although
faithful
replication is
essential,
change is
sometimes needed
when conditions
change.
Prokaryotes have
ways to get
additional
genetic material
from other
prokaryotes.
This method is
called conjugation.
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In
addition to binary
fission, bacteria
sometimes share
genetic material by a
process called
conjugation. There
is a special set of
genes that allows some
cells to do this.
The
cells may have plasmids,
small circles of DNA,
floating in their
cytoplasm.
Sometimes they share
their plasmids with
other cells.
This
is how conjugation
works.
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Bacteria
are swimming freely in water.
Note
the loop of genetic material.
Note
the blue ribosomes
Note
the round orange plasmids.
Plasmids
are free floating little
loops of DNA.
They can reproduce themselves
independently.
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Gotcha!
One
of the bacteria sends
out a "grappling
hook" and catches the
other one!
This
little hook is called a pilus.
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The
pilus draws the bacteria
close to each other.,
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The
pilus becomes a tube and some
of the little plasmids (small
independent loops of 'DNA)
cross over from one cell to
the other cell.
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The
tube closes and the bacteria
go on their way with some
genetic material that they
did not have before.
These
genes may find their way into
the main DNA loop.
This
really happens! You
have heard of infections that
become resistant to penicillin
and that then pass their
resistance to other
infections and
diseases. This is how
they do it!
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There
are two other ways that cells can
pick up extra and DNA.
One is transformation In
transformation the cell absorbs DNA
that is floating around in its
environment.
In
transduction a cell is
invaded by a virus. A virus is
even smaller than a prokaryote, but
it also has DNA. Some of the
viral DNA may become part of the
genome of the prokaryote or the
archaean organism. Perhaps the
new DNA will help the organism to
survive, perhaps it will have no
effect, perhaps it will put the cell
at a disadvantage Only
time will tell.