What is The nucleus?

The nucleus holds the chromosomes as chromatin, DNA wound on histone proteins (Chapter 17). It is bounded by the nuclear envelope, two membranes, the outer one continuous with the endoplasmic reticulum, pierced by nuclear pores through which RNA and proteins pass in both directions under control. The nucleolus is the region where ribosomal RNA is made and ribosomes are assembled. The nucleus separates transcription (inside) from translation (outside), a separation prokaryotes do not have.