... nails. * Each human cell has a unique combination of proteins and other chemicals on its surface. The body will reject cells if the proteins on the surface are completely different. This is especially the case when an organ transplant is done, the body will reject an organ unless careful matching is done. Two amino acids join together to form a dipeptide. A chain of amino acids is known as a polypeptide. A protein consists of one or more polypeptides. The bond between two amino acids is called a peptide bond. This is formed between the carboxyl part of one amino acid to the amine group of another. They join together in a condensation reaction. The diagram to the right is an example of such a reaction: The structure of proteins can be studied on four levels. These are primary, secondary, tertiary and quaternary. Primary Structure The number and sequence of amino ...

See this essay or coursework document in full right now