Advanced Topic 945 of 1102 Analytical, Lab & Spectroscopy
Electrophoresis
Charged molecules separate in an electric field according to size and charge.
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In-depth explanation of Electrophoresis
Electrophoresis separates charged molecules by their migration through a medium under an applied electric field, with the migration rate depending on the charge-to-size ratio of each species. Molecules move toward the electrode of opposite charge at velocities that depend on their charge, size and shape, and the support medium, such as a polyacrylamide or agarose gel, acts as a molecular sieve. Sodium dodecyl sulfate denatures proteins and gives them a nearly uniform charge-to-mass ratio, so SDS-PAGE separates proteins mainly by molecular mass. Agarose gels are used for DNA fragments, which are separated by length because the phosphate backbone gives each base a similar charge. Capillary electrophoresis offers high speed and resolution.
Going deeper: Electrophoresis
Key ideas: Mobility mu = q/(6 pi eta r) for a sphere in free solution, so higher charge and smaller size move faster. Typical conditions: agarose 0.7 to 2 percent for DNA, polyacrylamide for proteins and small DNA, 5 to 10 V/cm. Use a buffer such as TAE or TBE and stain with ethidium bromide alternatives or Coomassie. Isoelectric focusing separates proteins by pI in a pH gradient, and migration stops at net charge zero.
Common mistakes and connections: Students forget that DNA is negatively charged, so it runs toward the positive electrode, and load samples at the wrong end. Running too long loses small fragments off the gel. Heat from high voltage causes smiling bands. Native and SDS gels give different information, since native retains charge and shape effects. Related to charge, ions in solution, isoelectric point and gel structure.
Visualization of Electrophoresis
On an agarose gel, DNA migrates farther the shorter it is, giving a roughly straight line of log size against distance used to size unknown fragments. The interactive lesson shows this as a live animation or chart.
Worked example and use case
DNA fragments from a restriction digest are sized on an agarose gel by comparison with a ladder.
Frequently asked questions about Electrophoresis
What is Electrophoresis?
Charged molecules separate in an electric field according to size and charge.
Is Electrophoresis a beginner, intermediate or advanced topic?
Electrophoresis is a advanced topic in Analytical, Lab & Spectroscopy. It builds on beginner and intermediate topics, so review those first if needed.
What should I learn before Electrophoresis?
Study these earlier topics in Analytical, Lab & Spectroscopy first: Detection Limit, Sampling, Quality Control.
What comes after Electrophoresis?
The next topics in Analytical, Lab & Spectroscopy are Centrifugation and Spectrophotometer Design.
Can I practise Electrophoresis with quizzes?
Yes. The interactive lesson includes a self-check question on Electrophoresis, and the Analytical, Lab & Spectroscopy quiz draws on every topic in this area.
Where Electrophoresis fits in Analytical, Lab & Spectroscopy
Electrophoresis is topic 69 of 99 in Analytical, Lab & Spectroscopy.