The Shape and Structure of Proteins From a chemical point of view, proteins are by far the most structurally complex and functionally sophisticated molecules known. This is perhaps not surprising, once one realizes that the structure and chemistry of each protein has been developed and fine-tuned over billions of years of evolutionary history. The Shape of a Protein Is Specified by Its Amino Acid Sequence There are 20 types of amino acids in proteins, each with different chemical properties and which give each amino acid its unique properties: the 20 different amino acid side chains. Some of these side chains are nonpolar and hydrophobic (“water-fearing”), others are negatively or positively charged, some are reactive, and so on. A protein molecule is made from a long chain of these amino acids, each linked to its neighbor through a covalent peptide bond. Proteins are therefore also known as polypeptides . Each type of protein has a unique sequence of amino acids. Many thousands of different proteins are known, each with its own particular amino acid
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