- This can be used to determine the sizes of DNA fragments in experiments
- Methods to make the DNA visible:
- Autoradiography: radioactive DNA; gel exposed to a photographic plate to
make bands visible
- Stain with ethidium bromide: fluorescent dye- must be handled carefully
because it is carcinogenic
- Stain with methylene blue- not as sensitive as ethidium, but safer
- Example:
- The example shows calibration standards, running from 0.6 to 23 kilobases,
on the left
- The unknown has 2 bands, of approximately 7.5 and 2.1 kilobases
Restriction Enzymes Can be Used to Make Recombinant DNA
- If a plasmid and the DNA sample of interest have some of the same
restriction sites the DNA can be inserted into the plasmid
- Steps in making recombinant DNA:
- Cut both the plasmid and the DNA sample with the same restriction enzyme
- The sticky ends are complementary and will hydrogen bond to each other
- Make the attachment permanent with the enzyme DNA ligase (catalyzes
formation of phosphodiester bonds
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- The blue dot on the plasmids represents the ampicillin-resistance gene
- Similar methods can be used to make recombinant DNA with bacteriophage
- Recombinant DNA was first made by these methods by Herbert Boyer (Stanford
University) and Stanley Cohen (UC, San Francisco) in 1973
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