IgG contains two small and two large polypeptide chain. A preparation of IgG was incubated with SDS, heated, and submitted to SDS polyacrylamide gel electrophoresis. Only one major band near the top of the gel was observed after staining. Explain these results.

The structure of immunoglobulin G (IgG) is basically of a protein nature, so the SDS is responsible for conferring a negative charge on the molecule and will cause it to migrate mostly to one side of the gel, which explains the result of the SDS polyacrylamide gel electrophoresis test.

Explanation:

IgG is an antibody synthesized by the immune system, responsible for the defense of the organism against the attack of biological agents. Its structure is predominantly high molecular weight protein, specifically glycoproteins.

SDS - sodium dodecyl sulfate - is a surface active agent, capable of breaking down the secondary and tertiary structures of proteins, but keeping its amino acid sequence intact. Additionally, SDS can confer a negative charge on IgG proteins.

During polyacrylamide gel electrophoresis, the negatively charged IgG proteic molecules -treated with SDS- migrate to the top of the gel according to its molecular weight, which explains why only one major band near the top of the gel was observed after staining.

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