Proper function by proteins require proper folding. It is not just stringing together amino acids but folding the string into the right configuration:-"A wide range of diseases are caused by an accumulation of misfolded proteins. Among the diseases are neurodegenerative diseases like Alzheimer's disease, Parkinson's disease and Huntington's disease. Other diseases include certain types of diabetes, inherited cataracts and cystic fibrosis."-http://www.sciencedaily.com/releases/2013/12/131209181101.htm