The nucleus is generally between 5 to 10 micrometers in diameter. The nucleus has long been called the control center of the cell because it houses DNA. The nucleus contains most of the genetic information in the form of DNA. DNA is the organic "code" that allows us to be who we are, have the characteristics we do. This DNA code called chromatin, condenses into chromosomes during mitosis. The nucleus has a membrane that is porous. The "pores" in the membrane allow for RNA, another type of nucleic acid, to leave the nucleus after being made from the DNA template. Both transfer RNA and ribosomal RNA is made in the nucleolus. The nucleolus resides within the nucleus. Look closely at this drawing. It depicts the endoplasmic reticulum being closely associated to the nucleus.