SDS-PAGE
Definition
PAGE run with sodium dodecyl sulphate. SDS coats proteins with uniform negative charge, so separation is by molecular weight alone.
- Full name
- Sodium dodecyl sulphate polyacrylamide gel electrophoresis
- Detergent role
- Coats proteins with uniform negative charge
- Separation basis
- Molecular weight alone
- Parent technique
- Polyacrylamide gel electrophoresis (PAGE)
Common questions
Why does coating proteins with uniform charge make SDS-PAGE separate by size rather than by native charge?+
Without SDS, proteins migrate through the gel according to their own intrinsic charge and shape, which varies unpredictably between proteins. SDS binds proteins in proportion to their length and swamps their native charge, so migration through the gel matrix is then governed almost entirely by molecular size.
What forensic applications rely on SDS-PAGE rather than native PAGE?+
SDS-PAGE is used where a protein's molecular weight itself is the diagnostic feature, such as characterizing venom components, distinguishing species by muscle or blood protein banding patterns, or as a preparative step before further analysis like mass spectrometry.
Does SDS-PAGE preserve a protein's biological activity for later testing?+
No, SDS denatures proteins by disrupting their folded structure, so any assay that depends on native conformation or enzymatic activity must be done before SDS-PAGE or by a separate native electrophoresis method instead.
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...
- Electrophoretic Mobility (μ)
- Velocity of a charged particle per unit electric field, μ = v/E. Depends on charge, size, shape and the viscosity of the...
- 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.