The nucleoplasm, also known as karyoplasm, is the type of protoplasm that makes up the cell nucleus, the most prominent organelle of the eukaryotic cell. It is enclosed by the nuclear envelope, also known as the nuclear membrane. The nucleoplasm resembles the cytoplasm of a eukaryotic cell in that it is a gel-like substance found within a membrane, although the nucleoplasm only fills out the space in the nucleus and has its own unique functions. The nucleoplasm suspends structures within the nucleus that are not membrane-bound and is responsible for maintaining the shape of the nucleus. The structures suspended in the nucleoplasm include chromosomes, various proteins, nuclear bodies, the nucleolus, nucleoporins, nucleotides, and nuclear speckles.
An example of the sodium-potassium pump, a P-type ATPase, which controls the ionic gradient across the cell membrane and the nuclear envelope as well as the ionic makeup of the nucleoplasm through the selective pumping of sodium and potassium ions.
The cell nucleus is a membrane-bound organelle found in eukaryotic cells. Eukaryotic cells usually have a single nucleus, but a few cell types, such as mammalian red blood cells, have no nuclei, and a few others including osteoclasts have many. The main structures making up the nucleus are the nuclear envelope, a double membrane that encloses the entire organelle and isolates its contents from the cellular cytoplasm; and the nuclear matrix, a network within the nucleus that adds mechanical support.
HeLa cells stained for nuclear DNA with the blue fluorescent Hoechst dye. The central and rightmost cells are in interphase, thus their entire nuclei are labeled. On the left, a cell is going through mitosis and its DNA has condensed.
An image of a newt lung cell stained with fluorescent dyes during metaphase. The mitotic spindle can be seen, stained green, attached to the two sets of chromosomes, stained light blue. All chromosomes but one are already at the metaphase plate.
Oldest known depiction of cells and their nuclei by Antonie van Leeuwenhoek, 1719
Drawing of a Chironomus salivary gland cell published by Walther Flemming in 1882. The nucleus contains polytene chromosomes.
