DNA Sequencing

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Author:
camturnbull
ID:
270576
Filename:
DNA Sequencing
Updated:
2014-04-14 20:01:03
Tags:
Biology Genes camturnbull
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Description:
AQA BIOL5 DNA sequencing
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  1. On what does DNA sequencing rely?
    The premature ending of DNA synthesis by using modified DNA nucleotides known as terminators on which the DNA polymerase enzyme can add no further nucleotides
  2. Describe stage 1 of DNA sequencing
    PCR is used to make large amounts of the DNA that is to be sequenced
  3. Describe stage 2 of DNA sequencing
    • Four reactions are set up containing:
    • Many single stranded copies of the DNA that is to be sequenced 
    • DNA polymerase 
    • A single stranded primer that binds to complementary bases of DNA of interest and initiate replication. The fragments of DNA can be detected by the radioactive nucleotides contained within the primer 
    • The four normal nucleotides mixed with a modified version of one of the nucleotides known as the terminator. The other three reactions are the same, only containing a modified version of one of the other nucleotides
  4. Describe stage 3 of DNA sequencing
    • The DNA polymerase attaches the nucleotides together after they have hydrogen bonded to the DNA until a modified terminator nucleotide is added when replication will halt 
    • As the nucleotides are added at random, the enzyme will be halted at different places depending on where the terminator is added
  5. Describe stage 4 of DNA sequencing
    The fragments are separated using gel electrophoresis
  6. Describe stage 5 of DNA sequencing
    • Once the gel has run, an unexposed photographic film is laid on the gel 
    • The radioactive fragments create dark shadows on the film corresponding to the positions of the DNA fragments in the gel 
    • This is known as autoradiography

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