Amino Acid

Although more than 300 different amino acids have been described in
nature, only twenty are commonly found as constituents of mammalian proteins. Each amino acid(except for proline) has a carboxyl group, an amino group, and a distinctive side chain ("R-group") bonded to the a-carbon atom . At physiologic pH (approximately pH = 7.4), the carboxyl group is dissociated, forming the negatively charged carboxylate ion (-COO ), and the amino group is protonated (-NH3+).

Each of these amino acids has a nonpolar side chain that does not bind or give off protons or participate in hydrogen or ionic bonds. The side chains of these amino acids can be thought of as "oily" or lipid-like, a property that promotes hydrophobic interaction.

These amino acids have zero net charge at neutral pH, although the side chains of cysteine and tyrosine can lose a proton at an alkaline pH. Serine, threonine, and tyrosine each contain a polar hydroxyl group that can participate in hydrogen bond formation. The side chains of asparagine and glutamine each contain a carbonyl group and an amide group, both of which can also participate in hydrogen bonds.

The amino acids aspartic and glutamic acid are proton donors. At neutral pH, the side chains of these amino acids are fully ionized, containing a negatively charged carboxylate group (-COO"). They are,therefore, called aspartate or glutamate to emphasize that these amino acids are negatively charged at physiologic pH.

The side chains of the basic amino acids accept protons. At physiologic pH the side chains of lysine and arginine are fully ionized and positively charged. In contrast, histidine is weakly basic, and the free amino acid is largely uncharged at physiologic pH. However, when histidine is incorporated into a protein, its side chain can be either positively charged or neutral, depending on the ionic environment provided by the polypeptide chains of the protein.

All free amino acids, plus charged amino acids in peptide chains, can serve as buffers.

Amino acids are the building blocks of protein. When you eat a food that is high in protein, your body digests the protein into individual amino acids and short links of amino acids that are small enough to be absorbed into the bloodstream. The primary functions of amino acids are to build and repair muscle tissue, but the benefits go beyond that. These things produce chemicals that allow our brains to function at its highest potential