Electrophoretic Mobility (μ)
Definition
Velocity of a charged particle per unit electric field, μ = v/E. Depends on charge, size, shape and the viscosity of the support medium.
- Symbol
- μ
- Formula
- μ = v/E
- Depends on
- Charge, size, shape, medium viscosity
- Field
- Electrophoresis
Common questions
Why do two molecules with the same net charge sometimes have different electrophoretic mobility?+
Mobility also depends on the size and shape of the molecule and the friction it experiences moving through the support medium, so a smaller or more compact molecule can move faster than a larger one even when their net charge is identical.
How is electrophoretic mobility used practically in forensic serology or DNA work?+
Differences in mobility separate proteins, isoenzymes, or nucleic acid fragments into distinct bands or zones on a gel, and comparing the mobility pattern of a questioned sample against a known reference is the basis for typing and identification in electrophoretic methods.
Related terms
- Agarose
- Polysaccharide gel from seaweed. Large pore size, used for nucleic acids and large proteins. Standard for DNA submarine gels.
- Capillary Electrophoresis (CE)
- A separation technique that resolves DNA fragments by size through a polymer-filled glass capillary under an applied electric field. Single-base resolution is...
- IEF (Isoelectric Focusing)
- Electrophoresis across an immobilised pH gradient. Each protein migrates until it reaches its pI and stops. Very high resolution; used in haemoglobin...
- Immunoelectrophoresis
- A two-step technique: proteins are first separated by electrophoresis in agar gel, then antiserum diffuses from a parallel trough and forms precipitin...
- Isoelectric Point (pI)
- pH at which a molecule (usually a protein) carries zero net charge and stops migrating. The basis of isoelectric focusing (IEF).
- Polyacrylamide (PAGE)
- Cross-linked synthetic gel with tunable, smaller pore size. Used for proteins and small DNA fragments.
- Precipitin Arc
- Curved line of antigen-antibody precipitate that forms at equivalence in immunoelectrophoresis. Shape and position identify the antigen.
- SDS-PAGE
- PAGE run with sodium dodecyl sulphate. SDS coats proteins with uniform negative charge, so separation is by molecular weight alone.