Proteins have a variety of functions within a living cell. What are the possible functions of proteins, and how can proteins be so diverse?

Proteins perform a diverse range of functions for the cell.
For example they....:
1. Help in metabolism by providing structural support and by acting as enzymes, carriers, or hormones.
2. Provide energy for the body
3. Have a role in repair and maintenance
4. Have a role in the secretions of some hormones (insulin, for example, is a small protein)
5. Proteins form antibodies. They often work in conjunction with the other immune system cells like white blood cells.

Protein functions are so diverse because of the many unique three-dimensional structures protein polymers form.