Proteins are organic molecules found in large quantities in most living systems. Although proteins are used for many different functions, proteins are very similar in structure.
Proteins are generally large molecules containing hundreds of amino acids.
In living organisms, a protein is assembled into a long polypeptide chain by the linking of amino acids. This linear sequence of amino acids is called the primary structure. As the chain of amino acids is formed, various interactions begin to take place among the amino acids along the chain. Linus Pauling and Robert Corey discovered that H bonds could form between the slightly positive amino hydrogen of one amino acid and the slightly negative carboxyl oxygen of another amino acid. The regular, repeated configurations caused by H bonding between atoms of the polypeptide backbone is called the secondary structure.