PROTEINS, ENZYMES, & CHROMATOGRAPHY
2024-2025 EDVOTEK ® RESOURCE GUIDE
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How Does SDS-PAGE Separate Proteins?
After denaturation, the mixture of proteins is added into depres- sions (or “wells”) within a gel, and then an electrical current is passed through the gel. Because the SDS-protein complex has a strong nega- tive charge, the current drives the proteins through the gel towards the positive electrode. At first glance, a polyacrylamide gel appears to be a solid. On the molecular level, the gel contains channels through which the proteins can pass. Small proteins move through these holes easily, but large proteins have a more difficult time squeezing through the tunnels. Because molecules of different sizes travel at different speeds, they separate into discrete “bands” within the gel. After the current is stopped, the bands are visualized using a stain that sticks to proteins.
SDS polyacrylamide-gel electrophoresis, or SDS-PAGE, is a technique that is used to separate proteins according to their molecular weight. Proteins produce a unique challenge for electrophoresis be- cause they have complex shapes and different charges, which affect how they migrate through the gel. In order to accurately separate proteins by molecular weight and not by shape or charge, the secondary structure of the protein is unfolded using the anionic detergent sodium dodecyl sulfate (SDS) and a reduc- ing agent. The SDS molecules form a complex with the protein, negating its inherent charge. The reducing agent breaks covalent bonds that link protein subunits.
RELATED EQUIPMENT
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