Amino Acids: Biochemistry and Nutrition

Proteins are large, complex molecules essential for the normal function of the human body, specifically in the structure, function and regulation of tissues and organs. They are made up of hundreds of smaller units called amino acids that are attached to one another by peptide bonds, forming a long chain. Amino acids form polymers through a nucleophilic attack by the amino group of an amino acid at the electrophilic carbonyl carbon of the carboxyl group of another amino acid. The carboxyl group of amino acid must first be activated to provide a better leaving group than OH-. The resulting link between amino acids is an amide link, which biochemists call a peptide bond. In this reaction, water is released. In reverse reaction, the peptide bond can be cleaved by water (hydrolysis). When two amino acids link together to form an amide link, the resulting structure is called a dipeptide. Likewise, we can have tripeptides, tetrapeptides, and other polypeptides. At some point, when the structure is long enough, it is called protein. There are many different ways to represent the structure of a polypeptide or protein, each showing different amount of information. The key elements of an amino acid are carbon, hydrogen, oxygen, and nitrogen, though other elements are found in the side-chains of certain amino acids. They can be classified according to the core structural functional groups’ locations as alpha- (?-), beta- (?-), gamma- (?-) or delta- (?-) amino acids; other categories relate to polarity, pH level, and side-chain group type (aliphatic, acyclic, aromatic, containing hydroxyl or sulfur, etc.). In different forms of proteins, amino acids comprise the second largest component (water is the largest) of human muscles, cells and other tissues. Outside proteins, amino acids perform critical roles in processes, such as neurotransmitter transport and biosynthesis. In biochemistry, amino acids having both the amine and the carboxylic acid groups attached to the first (alpha-) carbon atom have particular importance. They are known as 2-, alpha-, or ?-amino acids (generic formula H2NCHRCOOH in most cases, where R is an organic substituent known as a “side-chain”); often the term “amino acid” is used to refer specifically to these. Many important proteinogenic and non-proteinogenic amino acids also play a critical non-protein roles within the body. Because of their biological significance, amino acids are important in nutrition and are commonly used in nutritional supplements, fertilizers, and food technology. Industrial uses include the production of drugs, biodegradable plastics, and chiral catalysts.