Nuclear Structures, Nuclear Functions
The nucleus is a large membrane-bound cell organelle which houses the chromosomes and which occupies roughly 10% of the volume of all eukaryotic cells. The nucleus is separated from the rest of the cell and the cytoplasm by a double membrane known as the nuclear envelope. The outer layer of the nuclear membrane is studded with small openings called nuclear pores, which allow for the controlled movement of selected molecules in and out of the nucleus. Most of a eukaryotic cell's DNA is found in the chromosomes of the nucleus, while a very small amount of DNA is present in the mitochondria. All plant and animal cells with a nucleus and known as eukaryotic cells, (meaning true nucleus) while bacterial cells which lack a nucleus are known as prokaryotic cells.