Nucleus

The nucleus is, of course, the 'brain' of the cell. It controls all the functions of the cell and in it it holds the genetic information that's called chromatin. Also inside the nucleus is the nucleolus, an organelle that synthesizes protein-producing macromolecular assemblies called ribosomes.

The nucleus itself is enclosed in a double-layered membrane called the nuclear envelope. This envelope is filled with holes called nuclear pores that allow specific molecules to pass back and forth between the nucleus and the cytoplasm.