Random coil

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A random coil is a polymer conformation where the monomers are arranged at random. Many simple polymers such as polyethylene inhibit only this conformation, more complex polymers with varying chemical groups attached to its backbone, such as proteins, self-assemble into well defined structures.

Proteins or segments of proteins that completely lacks secondary structure inhibit the random coil conformation. In random coil, the only fixed relationship between amino acids is that between adjacent residues through the peptide bond. As a result, random coil can be detected from the absence of the signals in a multidimensional nuclear magnetic resonance experiment that depend on particular peptide-peptide interactions. Likewise in the images produced in crystallography experiments, pieces of random coil appear simply as an absence of "electron density" or contrast. Random coil is also easily distinguished by circular dichroism. Denaturing reduces a protein entirely to random coil.