As you learned in BIO101, the cell nucleus is the storage area for all genetic material and constantly full of activity. The nucleus in fact contains not only DNA, but RNA and protein as well. This unit will take a detailed look at chromosomes, the cell nucleus, gene expression, and expression regulation. When we refer to “expression regulation,” we are talking about the fact that not all genes are expressed in the cell at the same time. After all, though a liver cell and a nerve cell have the same genome (and thus the same DNA), they look and act completely differently. How does this happen? The answer is regulated gene expression!