Answer to Question #190596 in General Chemistry for Alex

Question #190596

Sodium dodecyl sulfate (SDS) is a detergent used in polyacrylamide gel electrophoresis (PAGE), a

laboratory technique used in separating protein samples according to their molecular weight—smaller proteins travel faster through the gel and end up closer to the bottom, compared to larger proteins, which usually stay closer to the top. Detergents are described to be amphiphilic molecules, as they possess both a non-polar group (usually long hydrophobic functional moieties like long-chain alkyl groups) and a polar group (which may be polar like -OH or charged like phosphate groups).

  1. Describe the interaction of SDS with a protein molecule. How will a detergent like SDS affect the protein’s structure?
  2. How will SDS affect the overall charge of the protein? Will it affect the overall charge at all?
Expert's answer


Detergents can be denaturing or non-denaturing with respect to protein structure. Denaturing detergents can be anionic such as sodium dodecyl sulfate (SDS) or cationic such as ethyl trimethyl ammonium bromide. These detergents totally disrupt membranes and denature proteins by breaking protein–protein interactions. The SDS has a hydrophobic tail that interacts strongly with protein (polypeptide) chains. The number of SDS molecules that bind to a protein is proportional to the number of amino acids that make up the protein. Each SDS molecule contributes two negative charges.

2.Since SDS carries a highly negative charge and has a hydrophobic tail that interacts strongly with the protein or polypeptide chains, it can impart relatively equal negative charge to all the protein molecules in the sample. Keep in mind that each SDS molecule binds with two amino acids.

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