Nucleolus

The nucleolus is a structure that is not bound by a membrane and is found within the nucleus. It's function is thought to be the manufacture of the subunits that combine to form ribosomes, the structures that produce the cell's proteins.The size of nucleolus depends on the protein synthesis requirements of the cell. In cells that produce large amounts of protein, and therefore need a significant number of ribosomes, the size of the nucleolus is considerable.