a single covalent bond between the sulfur atoms to two
amino acids called cysteine.
because it is a covalent bond, the disulfide bond
can be considered as part of the primary structure
of a protein.
they are very important in determining the tertiary
structure of proteins
they are very important in determining the quartenary
structure of some proteins. An very prominant example would be the role
of disulfide bonds in the structure of antibody molecules.