Index >> Cellular Components >> Protein Structure

In addition to this, the carboxyl oxygen of one peptide group can hydrogen bond to an amide hydrogen of a different peptide group, Depending upon the location of the amides which participate in hydrogen bonding, the pattern of symme­try of the peptide chain assumes a helical structure.

The structure and symmetry created by the various forces is caned the secondary structure of the polypeptide. Linneaus Pauling and Robert Corey in 1950 first proposed the a helical secondary structure of Polypeptides. In theory, the helix shows a screw type symmetry in either right handed or a left handed direction, which varies with different proteins. The number of amino acid residues per turn of the helix is 3.6

The multimers may be homo or hetero multimers. The structure of a protein Composed of two or more monomeric subunits is called the quaternary structure. In its simplest form, quaternary structure is the shape of the multimeric molecules and the shape of the multimer depends on tree number of monomers, the size and shape of each monomer, and on the nature of the monomer-monomer inter action. The quarternary structure of most multimers can be destroyed without disturbing the tertiary, secondary or primary structures. The dissociation is often reversible. The aggregation process (also called assembly) is directed by the tertiary structure of the monomers and does not need any catalytic function. Such self-assembly processes are wide spread in biological system. Most biologically active proteins are today known to be aggregates with tertiary structures In summary, the primary structure of the peptide is determined by the sequence of amino acids. This contributes to the second­ary structure and both contribute to the tertiary structure of the pro­tein. For each functional protein, these structures are defined and any alteration in this may lead to non function.