From Seed to Seed:
Plant Science for K-8 Educators

Proteins. Proteins are large molecules that are constructed from "building blocks" different from those that make up carbohydrates and oils. Proteins are formed by the combination of nitrogen-containing molecules called amino acids. There are about 20 different amino acids, and the type and sequence of the amino acids determines the type of protein molecule.

Plants use proteins in several ways: to store energy, as part of their structural framework, and as enzymes. Enzymes are a very important type of protein. Every chemical reaction that takes place in a living organism depends in part on the action of an enzyme. Without enzymes, there would be no metabolism, and no life.

The human body can synthesize all but eight of the amino acids it needs. The eight that we cannot make are called the essential amino acids. A diet deficient in any one of these amino acids results in a protein deficiency-no matter how much of the other amino acids you ingest.

Most plants are deficient in at least one type of essential amino acid. Grains, for example, are an extremely important food source worldwide, but they are generally deficient in the amino acids lysine and tryptophan. Fortunately, legumes have plenty of these amino acids. Most legumes, however, are deficient in the amino acid methionine. Fortunately, grains contain this one.