Each protein in the biological system has a unique 3-D structure and has specific biological activity. This is called native form of a protein. When a protein in its native form is subjected to physical changes such as change in temperature, pH, etc. hydrogen bonds are broken. Due to cleavage of hydrogen bonds, unfolding of protein molecule occurs and the protein loses its biological activity. This loss of biological activity is called denaturation. During denaturation, 2-degree and 3-degree structures of proteins are destroyed but 1-degree structure remains intact. As a result of denaturation, globular proteins are converted into fibrous proteins. In other words, denaturation leads to coagulation. That is why coagulated proteins are also called denaturated proteins.