A2 OCR Biology 2.2.9 DNA manipulation and probes

just a little revision for the spread 2.2.9

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Emily Summers
Electrophoresis Separation of different lengths of DNA fragments in a mixture is
achieved as negatively charged fragments move towards the positive electrode (anode)
from the cathode, shorter fragments pass more freely through the gel so move further in
the fixed time period.
1. Treat DNA samples with restriction enzymes to cut them into
2. Place the DNA sample into wells cut into the cathode end of the
3. Immerse the gel into a tank containing buffer solution, and pass an electric
current through the solution for a fixed time (normally 2hrs)
4. The DNA has a negative charge due to the phosphate groups it contains, so the
fragments are attracted to the anode.
5. Shorter lengths of DNA move faster than longer lengths
6. The position of fragments can be seen by staining the DNA molecules

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Emily Summers
DNA probes are short, single stranded pieces of DNA which are about 5080 nucleotides
long, that is complementary to a section of the DNA being investigated.
Labelling the Probe:
Using a radioactive marker 32
P in the phosphate groups forming the strand, so the
location can be revealed by exposure to photographic film
Using fluorescent marker that emits colour on exposure to UV light. Fluorescent
markers can also be used in automated DNA sequencing.…read more


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