ABSTRACT
Proteins, saccharides, and nucleic acids are three common polymers and are vital substances found in all living organisms. Among them, proteins have the most diversified physiological functions. As building blocks, they are present in all living cells and involved in the construction of all tissues such as skin, muscle, bone, nerve and blood. As enzymes or hormones, they catalyze and regulate universal chemical reactions in a living body. As antibodies, they help to defend against attack by many pathogens. Almost every protein has a different function, although there is some overlapping of jobs. For example, hemoglobin in red blood cells can transport oxygen, a substance vital for the continuance of life, to every cell in the body.
