Biotechnology will move through the gel and towards the

Biotechnology poster

 

Gel
electrophoresis

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Gel electrophoresis is a
technique used to separate fragments of DNA, RNA or proteins by their length. Gel
electrophoresis is most commonly used for separating DNA fragments and will
therefore be discussed in most detail on this poster. In gel electrophoresis
for DNA sequences, restriction enzymes are used to cut the sequence at certain
combinations of nitrogenous bases. This gives rise to a number of DNA sequences
that can then be profiled using a gel made of a polysaccharide called agarose. The
agarose gel contains small pores, which the fragments of DNA can travel through
and therefore be separated. The DNA fragments are placed into the gel along
with a ladder of fragments of DNA of known lengths that provide a control to
the test.

 

These samples of DNA are moved
through in the gel using an electric current. As DNA (and RNA) is negatively
charged, and sequences will have the same charge per mass, shorter sequences
will move through the gel and towards the positive electrode at the bottom of
the well more quickly than longer fragments. This creates columns of DNA
fragments that can now be examined. However, when separating proteins based on
their lengths, an additional process is required as proteins are not negatively
charged. When using gel electrophoresis to separate proteins, researchers must
first mix the proteins with a detergent called sodium dodecyl sulfate. This
treatment makes the proteins unfold into a linear shape and coats them with a
negative charge.

 

The bands found in the gel can be
visualized using a DNA-binding dye to stain the gel and UV light, which makes
bands of DNA glow in the gel. Using the ladder of fragments of known base pairs
lengths makes it possible to identify the lengths of the bands that are being
tested.

 

Gel electrophoresis has a wide
range of applications in the real world. It is very commonly used in forensic science
to match the DNA of suspects to that found at crime scenes. Here, the DNA of a
suspect will be used in the ladder of fragments that act as the control for the
experiment. If the DNA in the ladder matches that of the sample, then the two
originate from the same person. Gel electrophoresis also plays and important
role in research. For example, ordering DNA and RNA strands by length allows
researchers to study them at a molecular level far more easily. Geneticists use
this technique to obtain a clearer picture of DNA and to prepare DNA for genetic
engineering and cloning.

 

 

Polymerase Chain Reaction

 

In many cases, only a small
sample of DNA is available for testing. When this sample isn’t sufficient for
these experiments to be performed, DNA needs to be multiplied. This is done by
a process known as Polymerase Chain Reaction (PCR).

 

PCR is a common laboratory
technique used to make millions or even billions of copies of a particular
region of DNA. This allows a small sample of DNA to be analyzed through
sequencing or gel electrophoresis.

As with DNA replication in an
organism, PCR requires a DNA enzyme that makes new strands of DNA from the
template strand. The DNA polymerase enzyme typically used in PCR is Taq
polymerase, named after the heat-tolerant bacterium from which it is obtained
(Thermus aquaticus). This enzyme is used as T. aquaticus lives in hot springs
and hydrothermal vents, which means its DNA polymerase is very heat-stable and
most active at around 70°C.
This is useful as high temperatures are constantly used in PCR to denature the
template DNA or separate its strands.