Peptide folding is the process by which a peptide structure assumes its functional shape or conformation. By coiling and folding into a specific three-dimensional shape, the peptides can perform their biological function. The amino acids with hydrophobic side chains tend to end up clustered at the core of the structure so that they are out of contact with water. Covalent disulfide bridges can affect the shape of a protein. Protein folding is a spontaneous process because the Gibbs free energy is negative.