Tertiary Structure

Protein Structure Tutorials

Primary Structure

Secondary Structure

Tertiary Structure

Quaternary Structure

Tertiary Structure: The Overall 3-Dimensional Shape of a Protein

A protein needs to adopt a final and stable 3-dimensional shape in order to function properly. The Tertiary Structure of a protein is the arrangement of the secondary structures into this final 3-dimensional shape.

The sequence of amino acids in a protein (the primary structure) will determine where alpha helices and beta sheets (the secondary structures) will occure. These secondary structure motifs then fold into an overall arrangement that is the final 3-dimensional fold of the protein (the tertiary structure).Each unique sequence of amino acids gives rise to a unique protein type, with a unique shape and function.

A summary of primary, secondary and tertiary structure is shown below.

Forces That Drive Tertiary Structure

Most proteins fold into their tertiary structure in an aqueous environment - a cell is, after all, 60% water. The chemical properties of the various R-groups (sidechains) of the amino acids within the protein chain will influence the way that the protein folds in its environment.

When a protein is surrounded by water:

Hydrophobic amino acids will move away from the water and bury themselves in the center of the protein.
Hydrophilic amino acids will interact with the water molecules, and thus tend to be located on the outer surface of the protein.
Basic (positvely charged) amino acids and
Acidic (negatively charged) amino acids create salt bridges, or electrostatic interactions, to further stabilize the tertiary structure.
Cysteines may form a disulfide bridge, further stabilizing the protein.

Click the buttons below to see each of these four groupings of amino acid types shown in the insulin protein in the display to the right. Click Here to download a chart summarizing all 20 amino acids and their R-group shapes.

Hydrophobic	Hydrophillic
Positive and Negative	Cysteine

The Structure-Function Relationship

Proteins are amazing molecules because they come in a huge variety of sizes and shapes; each shape suited to perform a specific task. The primary sequence of amino acids in a protein determines its 3-dimensional shape which, in turn, determines how the protein will function. This structure-function relationship is key to appreciating proteins and protein structure.

The same sequence of amino acids in an amino acid chain will fold into the same 3-dimensional shape each time it is made, allowing the body to produce millions of identical copies of any particular type of protein. This pattern is due to the properties of its unique sequence of amino acids (primary structure). As long as the sequence of amino acids is the same, the protein will fold into the same 3-dimensional shape.

Reseaching Protein Structures

If a protein does not fold correctly it will not function properly. Therefore, researching a protein's structure is very important when trying to understand what it does and how it works.

When scientists study a protein they must first determine the sequence of amino acids in the protein chain (primary structure). They use this sequence to predict the presence of any alpha helices or beta sheets (secondary structure). They can then use X-ray crystallography and NMR to determine a protein's full 3-dimensional shape (tertiary structure). Knowing the tertiary structure of a protein is often crucial to understanding how it functions and how to target it for drug therapy or other medical uses.

Move on to Quaternary Structure