The Structure of Proteins Introduction Campbell and Farrell define proteins as polymers of amino acids that have been joined covalently through peptide bonds to form chains of amino acids (61). A short chain of amino acids composed of thirty amino acids forms a peptide, while a longer chain of amino acids forms a polypeptide or protein. Each of the amino acids that make up a protein has a fundamental structure that includes a central carbon or alpha carbon bonded to a hydrogen element, an amino group, a carboxyl group, and a unique side chain or R group (Campbell and Farrell 61). Proteins perform myriad functions both inside and outside cells. These functions include structural roles (cytoskeleton), transport of molecules and ions across membranes, catalysis (enzymes), and hormonal roles. Proteins have structural features that can be described at four levels of complexity. This article summarizes the structure of proteins. Protein Structure Bettelheim, Brown, Campbell, and Farrell view proteins as intricate three-dimensional entities whose structural features can be discerned at four levels of increasing complexity (599). These levels are the primary, secondary, tertiary and quaternary levels of structure. The primary structure constitutes the simplest structures among the four levels. Levels of structure become more complex from the level of secondary to more organized quaternary protein structure.1. Primary structure of proteins Bettelheim, Brown, Campbell, and Farrell define the primary structure of proteins as the series of amino acid groups in a polypeptide chain that have been joined via peptide bonds forming the covalent structure of proteins (599). This structure usually determines the three-dimensional... middle of the paper... conclusion, proteins have four structural characteristics including primary, secondary, tertiary and quaternary protein structure. Tertiary, quaternary, and secondary structures are the result of protein stabilization by electrostatic, covalent, hydrophobic, or hydrogen bonds. These structures are those that determine the functions of proteins through their interactions with other molecules. The function of a protein can be changed through denaturation, a permanent and irreversible process in which it is exposed to heat or extreme pH values. Works Cited Bettelheim, Frederick, William Brown, Mary Campbell, and Shawn Farrell. Introduction to general, organic and biochemistry. 9th ed. Belmont, CA: Brooks/Cole Cengage Learning, 2010. Print. Campbell, Mary and Shawn Farrell. Biochemistry. 7th ed. Belmont, CA: Brooks/Cole Cengage Learning, 2011. Print.