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We can make
exact genetic copies of
whole organisms, cells or
pieces of DNA. These copies
are called clones. A clone
is a copy of a plant, animal
or micro-organism derived
from a single common
ancestor cell or organism.
Clones are genetically
identical.
A photograph
of DNA amplified using PCR
However, the word 'clone'
can also be applied to
genes. A gene is said to be
cloned when its sequence is
multiplied many times in a
common laboratory procedure
called polymerase chain
reaction (PCR).
To study genes,
researchers need large
amounts of
DNA to work with. PCR
copies the cell’s natural
ability to replicate its DNA
and can generate billions of
copies within a couple of
hours.
There are four main
stages:
- The DNA to be copied
is heated, which causes
the paired strands to
separate. The resulting
single strands are now
accessible to short
lengths of DNA called
primers. Primers match a
short section of the DNA
to be copied.
- Large amounts of
primers are added to the
single strands of DNA. The
primers bind to matching
sequences along the DNA
sequence, in front of the
gene that is to be copied.
The reaction mixture is
then cooled. This allows
double-stranded DNA to
form again. Because of the
large amounts of primers,
the two strands will
always bind to primers,
instead of to each other.
- DNA polymerase is
added to the mixture. This
is an enzyme that makes
DNA strands. It can
synthesise strands from
all the DNA primer
combinations and
dramatically increases the
amount of DNA present. One
enzyme used in PCR is
called Taq
polymerase which
originally came from a
bacterium that lives in
hot springs. It can
withstand the high
temperature necessary for
DNA strand separation and
therefore, can be left in
the reaction and still
functions.
- The above steps are
repeated until enough DNA
is obtained.
This whole process is
automated and happens in a
couple of hours. The
reaction occurs in a small
tube placed inside a
specialised machine that can
make the big temperature
adjustments quickly.
Researchers use the many
gene copies to research the
function of the gene. |
