Proteins are chains of amino acids that fold into three-dimensional shapes. The shape of the protein is very important to its function and the three-dimensional structure is specified by an amino acid sequence. The structure of proteins has 4 levels of organization called primary, secondary, tertiary and quaternary. Proteins are first made as a primary sequence composed of a linear sequence of amino acids connected by peptide bonds that continue to fold into secondary, tertiary, and finally quaternary structures. Twenty different amino acids are incorporated into proteins, the amino acid sequence of a protein is called its primary structure (Loughlin, 2017). Say no to plagiarism. Get a tailor-made essay on “Why Violent Video Games Should Not Be Banned”? Get the original essay A primary structure is the simplest level of a protein's structure. It is a sequence of amino acids in a polypeptide chain. Each chain has its own set of amino acids assembled in a particular order with a typical basic chemical structure, as shown in Figure 1 below. A central carbon atom (carbon a) bonded to a hydrogen atom, a basic amino group comprising one nitrogen atom and two hydrogen atoms (-NH2), a carboxyl group (-COOH ) and a specific side chain or R group made up of variable atoms. The R group gives each amino acid its identity: they can be polar, non-polar or even unchanged (Loughlin, 2017). The amino acids of a polypeptide are attached to each other by covalent bonds called peptide bonds, each bond forming a condensation. reaction. During protein synthesis, the carboxyl group of the amino acid at the end of the growing polypeptide chain reacts with the amino group of an incoming amino acid, releasing a water molecule. The resulting bond between the amino acids is a peptide bond. Due to the structure of amino acids, a polypeptide chain has two ends that are chemically distinct from each other. One end of the polypeptide chain has a free amino group called the amino terminus (N terminus) and the other end of which has a free carboxyl group called the carboxyl terminus (C terminus). Interactions between amino acids cause a protein to fold; from an amino acid sequence of a polypeptide to a three-dimensional structure of a mature functional protein (Loughlin, 2017). The two most important protein secondary structures, the alpha helix (a-helices) and the beta-sheet (ß-sheet) were predicted by Linus Pauling (1951) cited in Loughlin (2017, p. 9). Using X-ray diffraction (Loughlin, 2017, p.12, box 1.3), Pauling was able to determine the shape of proteins, thus discovering the spiral structure of proteins; the polypeptide backbone. He recognized that the folding of peptide chains, among other things such as steric hindrance, should maintain the bond angles and planar structure of the peptide bond while preventing atoms from approaching and repelling each other. . The two types of secondary structures, a helix and a β-sheet, are held in shape by hydrogen bonds, which form between the carbonyl (C=O) and the amine (NH) shown below, pulling the polypeptide chain in a helical structure allowing the side chain to emerge. and interact freely. The majority of protein characteristics are consistent with their secondary structures. They can be either fibrous, important in the formation of biological structures, or globular, spherical in shape with regions, 2017).