Protein Structure

Protein structure is the three dimensional arrangement of the atoms making up a protein, described in four recognized levels: the primary structure, the plain sequence of amino acids in the chain; the secondary structure, local folding patterns such as the alpha helix and the beta sheet held together by hydrogen bonds; the tertiary structure, the overall folded shape of one chain; and the quaternary structure, the arrangement of separate chains working together as one functional unit. X-ray crystallography, which reconstructs a molecule's atomic arrangement from the pattern its crystal casts when struck by X-rays, determined the majority of protein structures known today, beginning with Dorothy Hodgkin's determinations of penicillin in 1945, vitamin B12 in 1955 and insulin in 1969.