substances, humans have slightly more than twenty that are in use in protein building or in the synthesis of neurotransmitters. L-tryptophan, for example, is an amino acid used to make serotonin. For this reason, some providers will give L-tryptophan to depressed patients to build serotonin levels. Proteins and amino acids are the second largest molecular substance found in the human body. They can be classified according to their side chain, which can be aliphatic, acrylic, aromatic, or hydroxyl. Each side chain has a specific polarity that affects its solubility in aqueous solutions. The generic formulation of amino acids in humans is H2NCHRCOOH, where “R” refers to the side chain. All proteinogenic amino acids in humans are of the L-isomer type. There are twenty standard amino acids that are coded for by at least one gene (there can be more than one gene for a protein). There are two non-standard amino acids with no gene that codes for them which are synthesize in other ways. Selenocysteine, for example, is encoded by a stop codon and an SECIS segment, not a gene. Pyrrolysine is another example of a non-standard amino acid. Figure 2 shows the standard amino acids seen in nature:
Figure 2 Essential amino acids are not produced by the human body and must be consumed. There are nine of them and they include histidine, leucine, isoleucine, lysine, phenylalanine, methionine, threonine, valine, and tryptophan. Those that can be produced by the human body, including arginine, cysteine,
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