Quaternary Structure

Protein Structure Tutorials

Primary Structure

Secondary Structure

Tertiary Structure

Quaternary Structure: Protein Chains Combine to Make Protein Complexes

Secondary and tertiary structures are determined by a protein's sequence of amino acids, or primary structure. All proteins have primary, secondary and tertiary structure.

Some proteins are made up of more than one amino acid chain, giving them a quaternary structure. These multi-chain proteins are held together with the same forces as the tertiary structure of individual protein chains (hydrophobic, hydrophillic, positive/negative and cysteine interactions). Sometimes the various protein chains in a protein complex are identical and other times they are each unique.

Click on the proteins below to see their overall quaternary structure shown in the 3-dimensional display to the right. For each protein complex, the various chains are colored differently.

A Summary of Quaternary Structure

Proteins are long chains of amino acids that fold into complex 3-dimensional shapes.
Proteins come in an almost endless array of shapes and sizes, each acting like a specialized molecular machine that performs a specific molecular task.
Primary Structure  is the specific order of amino acids in a protein polypeptide chain. There are 20 different amino acids that can be incorporated into a protein chain, and have attributes (hydrophobic, hydrophilic, positive, negative, cysteine) that determine their final structure and function.
Secondary Structures are the alpha helices and beta sheets present in a folded protein's structure.
Tertiary Structure is the final shape of an entire amino acid chain. This shape is directly related to the function of the protein.
Quaternary Structure exists when more than one amino acid chain comes together to form a protein complex.