Protein Organization

During translation, a chain of amino acids emerging from the ribosome forms the primary protein structure. This peptide chain is held together by covalent bonds between two amino acids' amino and carboxyl ends.

Some amino acids make hydrogen bonds with their neighbors to form stable secondary structures such as alpha helices and beta-sheets.

Alpha-helices are spiral structures held together by hydrogen bonds between the carbonyl oxygen and amide hydrogen of every fourth amino acid residue of a polypeptide chain.

Beta-sheets are zigzag polypeptide structures formed when sections of the polypeptide chain interact sideways through hydrogen bonding.

Additional chemical interactions between distant amino acid side chains or the peptide backbone, such as hydrophobic forces, ionic bonding, and disulfide bridges, help the polypeptide fold into the tertiary structure. This 3D shape is the final functional form for many proteins.

If two or more polypeptide chains combine from the tertiary structure into a larger complex, a quaternary structure is created. These can be homomeric or heteromeric complexes with distinct cellular functions.