ABSTRACT

The name "protein" is derived from the Greek term proteos, which means "primary" or "to take place first." Protein was first discovered in the early 19th century, at which time scien­ tists described it as a nitrogen-containing part of food essential to life. While the elemental composition of the other energy nutrients is limited to carbon, oxygen, and hydrogen, pro­ tein also contains nitrogen (N) as well as sulfur (S). About one half of the dry weight of a typical human cell is attributed to protein. Some of the most significant roles for proteins are as structural components, contractile filaments, antibodies for immune responses, transporters, neurotransmitters, hormones, and enzymes.