26.2. Amino Acids and Proteins http://www.ck12.org
Amino Acids
Amino acidsare a class of molecules that contain both the carboxylic acid and amine functional groups. Amino
acids are key building blocks in biological systems. The most common biologically relevant amino acids have the
generic structure shown in theFigure26.3, in which a central carbon atom is connected to an NH 2 group, a CO 2 H
group, and a variable R group.
FIGURE 26.3
Generic amino acid.The only difference between one amino acid and another is the structure of the R group. In the simplest amino acid,
glycine, the R group is just a hydrogen atom. However, other common amino acids may involve alcohols, amines,
carboxylic acids, or aromatic rings.
Many amino acids can be linked together to form a long chain known as aprotein. These linkages are formed when
the carboxylic acid of one amino acid reacts with the amine of another to produce an amide (seeFigure26.4).
FIGURE 26.4
Peptide bond in protein.In the context of proteins, the newly formed bond between the carboxyl carbon and the amine nitrogen is referred to
as an amide bond or a peptide bond.
Nearly all biological proteins are constructed from a set of just 20 common amino acids. The names, abbreviations,