Could some one describe at least three different functions of proteins and explain how the shape of a protein affects its function?

A protein's shape is important because each protein has a specific action (or function) that it does, and it has to "fit" other molecules sometimes. For example, enzymes have active sites where the molucules bind to it. The active site is shaped to fit specific molecules. The enzyme sucrase only fits the sucrose molecule. Another example is hemoglobin, which does not have a nucleus because it functions as the carrying molecule for oxygen and needs the space for storage. Protein carrier molecules in cell membranes also have receptor sites that are shape specific to the molecule they are intended to transport.
A protein has 4 levels of structure and cannot funtion unless it has achieved the tertiary level.

1.some (most cases) protein acting as enzymes 2.some proteins help to maintain structural frame work (like virus core proteins)3.there are so many cannot generalize more,