Gel Electrophoresis (College Board AP® Biology): Study Guide

Gel electrophoresis

• Gel electrophoresis separates molecules according to their relative size and electrical charge

  • This technique can also be used with DNA, RNA and proteins

• During gel electrophoresis molecules are placed into a gel, and the different rates at which they move through the gel causes them to separate

• This separation of molecules occurs due to:

  • their electrical charge

    • There is an electrical charge across the gel, with a positive electrode at one end and a negative electrode at the other

    • DNA is negatively charged so DNA molecules move towards the positive electrode

  • their different sizes

    • Molecules move through the gel at different rates depending on their size

    • The tiny pores in the gel allow smaller molecules to move more quickly, while larger molecules move more slowly

    • It is possible to identify the size of fragments of unknown length by comparing the distance travelled with fragments of known size

• Gel electrophoresis can be used to produce DNA profiles, which can be useful for, e.g.

  • determining how closely related individuals or species are

  • forensic analysis, e.g. identifying DNA found at a crime scene

  • aiding in the process of DNA sequencing