Protein folding is the physical process by which a protein chain acquires its native 3-dimensional structure, a conformation that is usually biologically functional, in an expeditious and reproducible manner. It is the physical process by which a polypeptide folds into its characteristic and functional three-dimensional structure from random coil. Each protein exists as an unfolded polypeptide or random coil when translated from a sequence of mRNA to a linear chain of amino acids.
This polypeptide lacks any stable (long-lasting) three-dimensional structure. Amino acids interact with each other to produce a well-defined three-dimensional structure, the folded protein is known as the native state. The resulting three-dimensional structure is determined by the amino acid sequence.