Salam
Dear ..
the Answer of yr Q is :
The difference between peptide chains and proteins is based on function. If a peptide chain has a function (i.e. "does" something), it is a protein. For any protein, the ability of the molecule to perform its specific function is dependent upon its structure. Although the general structure for a protein is a peptide chain, the actual structure of the protein is not a linear chain of amino acids. Proteins fold into a specific three-dimensional conformation which is required for its specific function. If this three-dimensional folding is altered in any way, the activity of the protein can be lost and the protein will not work properly. Therefore, there is a intimate relationship between the structure and function of a protein. Do not forget this!!