The nucleus, the largest organelle in an eukaryotic cell, is the repository for the cell’s genetic information and the control center for the expression of that information. The boundary around the nucleus consists of two membranes (an inner one and an outer one) that form the nuclear envelope. Nuclear pores are small openings in the nuclear envelope that permit molecules to move between the nucleus and the cytoplasm. The nucleolus is a prominent structure within the nucleus. The nucle oplasm is the viscous liquid contained within the nucleus. In addition, the DNA-bearing chromosomes of the cell are found in the nucleus.