Nucleolus

This spherical structure within the nucleus is known as the nucleolus and is composed of DNA, RNA and proteins. It is the part of the cell that allows for the copying of DNA molecules. This is possible because the DNA present in the nucleolus codes for rRNA, otherwise known as nucleolar organizers. Proteins synthesized, or made, in the cytoplasm will enter through the nuclear pores and become associated, or connected, with the newly made rRNA in the nucleolus. Afterwards the ribosomal subunits migrate to the cytoplasm. The nucleolus disappears during cell division but reappears in the final stage of mitosis.