What is Protein?
Proteins in macromolecules are polymers, or substances that consist of a great amount of similar units bonded together. Nucleic acids are polymers, too! These "similar units" in proteins are called amino acids - organic compounds that contain amine and carboxyl functional groups (National Diagnostics). According to cK-12, "There are 20 different amino acids commonly found in the proteins of living organisms" (cK-12). When these amino acids bind together, they will form a quite long polypeptide. One or more of the long polypeptide chains make up a protein.
The Four Levels of Protein - picture from cK-12
There four levels included in protein - the primary protein structure, the secondary protein structure, the tertiary protein structure, and the quarternary protein structure. The primary protein structure, as you can see in the visual above, is simply the chain sequence of amino acids. The secondary protein structure is formed when the sequence of amino acids are connected by hydrogen bonds. The tertiary protein structure forms when, according to cK-12, "certain attractions are present between alpha helices and pleated sheets." Last, the quarternary protein structure is the final product of protein, which contains one or more chain(s) of amino acids (cK-12).
Who Discovered Protein?
Protein was discovered by Linus Pauling in the 1950's. Pauling contributed to Watson and Crick's discovery of the "double helix" DNA structure by discovering protein and its structure.