The overall three-dimensional arrangement of the secondary structures within a single peptide chain of a protein is called tertiary structure. There are several ways in which structures within a protein may be held together, such as:

• disulfide bonds - the thiol groups on the amino acid cysteine may be oxidized to form a covalent disulfide bond between different portions of the protein chain
• hydrogen bonding - hydrogen bonding may occur between polar groups on the sidechains of the protein structure
• salt bridges - an acidic sidechain and a basic sidechain may react to form a salt, forming a strong ionic interaction between the sidechains
• hydrophobic interactions - in aqueous solution, proteins will tend to keep their non-polar (hydrophobic) sidechains within the interior of the protein, away from water

 

Example #1 - Disulfide Bonds (the lysozyme structure)

In the structure below, there are four disulfide bonds between the eight cysteine amino acids. Look at the secondary structure to see how the disulfide bonds link together the helices and sheets.

Highlight	Cysteines	SS-bonds
Display	Secondary Structure

 

Example #2 - Hydrophobic Interactions (the myoglobin structure)

In the following structure, the sidechains have been color-coded as either hydrophilic (polar, water-loving) or hydrophobic (non-polar, water-hating). The backbone is in purple. Use the "Slice" button to view a cross-section of the interior of the protein. Note how the hydrophilic sidechains tend to be located on the outer surface while the hydrophobic sidechains are kept on the inside and stabilize the tertiary structure.