The Structure of ProteinsIntroductionCampbell and Farrell define proteins as polymers of amino acids that have been covalently joined by peptide bonds to form chains of amino acids (61). A short chain of amino acids comprising thirty amino acids forms a peptide, and a longer chain of amino acids forms a polypeptide or protein. Each of the amino acids comprising a protein has a fundamental design that includes a central carbon or alpha carbon bonded to a hydrogen element, an amino group, a carboxyl group, and a single side chain or the R group (Campbell and Farrell 61). Proteins perform a myriad of functions, whether inside or outside of cells. These functions include structural roles (cytoskeleton), transport of molecules and ions across membranes, catalysis (enzymes), and hormonal roles. Proteins have structural characteristics that can be described according to four levels of complexity. This article summarizes the structure of proteins. Protein Structure Bettelheim, Brown, Campbell, and Farrell view proteins as complex 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 structure levels. The primary structure constitutes the simplest structure among the four levels. The levels of structure become more complex from the secondary level to the most organized quaternary protein structure level.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 by peptide bonds forming the covalent backbone of proteins (599). This structure generally determines the three-dimensional dimension...... middle of article...... conclusion, proteins have four structural characteristics, including primary, secondary, tertiary, and quaternary protein structures. Tertiary, quaternary and secondary structures are the result of proteins stabilized by electrostatic, covalent, hydrophobic or hydrogen bonds. These structures are those which determine the functions of proteins through their interactions with other molecules. A protein's function can be changed by 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 biochemical chemistry. 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.