Protein: large organic compounds made of amino acids.
The name protein comes from the Greek πρώτα ("prota"), meaning "of primary importance" and were first described and named by Jöns Jakob Berzelius in 1838. However, their central role in living organisms was not fully appreciated until 1926, when James B. Sumner showed that the enzyme urease was a protein. The first protein structures to be solved included insulin and myoglobin; the first was by Sir Frederick Sanger who won a 1958 Nobel Prize for it, and the second by Max Perutz and Sir John Cowdery Kendrew in 1958. Both proteins' three-dimensional structures were amongst the first determined by x-ray diffraction analysis; the myoglobin structure won the Nobel Prize in Chemistry for its discoverers.
(Amino acids are molecules that contain both amine and carboxyl-funtional groups (alpha amino acids). There are 20 standard amino acids used by cells in protein biosynthesis and these are specified by the general genetic code.)
Proteins contain 4 levels of structure:
1). Primary: the amino acid sequence
2). Secondary: regularly repeating structures shaped by hydrogen bonds (most common are the alpha helix and the beta sheet)
3). Tertiary: the overall shape of a single protein molecule; the term "tertiary structure" is often used as synonymous with the term fold. Tertiary structured proteins are polypeptide chains consisting of secondary structured protein twisted and folded into a more 3-D structure.
4). Quaternary: contains a number of tertiary structured proteins as sub-units, which function as part of the larger assembly, or protein complex.