Now, because of this five member ring, this molecule is structurally restrictive. And that means this actually helps play a very, very important role in determining the structures of special types of proteins, as we'll see in future lectures. So all the proline is hydrophobic, and technically, it should belong to the hydrophobic side chain group. It is special in that it contains a side group that is bound to the alpha carbon and the nitrogen. So this is bound to this carbon here, as well as this nitrogen here. Now, the five member ring of Proline makes it structurally restrictive, allowing it to greatly influence the structure of special types of proteins.