Cell nucleus
HeLa cells stained for DNA with the Blue Hoechst dye. The
central and rightmost cell are in interphase, thus their entire
nuclei are labeled. On the left a cell is going through mitosis
and its DNA has condensed ready for division.
Schematic of typical animal cell, showing subcellular compon-
ents. Organelles: (1) nucleolus (2) nucleus (3) ribosome (4) ves-
icle (5) rough endoplasmic reticulum (ER) (6) Golgi apparatus
(7) Cytoskeleton (8) smooth ER (9) mitochondria (10) vacuole
(11) cytoplasm (12) lysosome (13) centrioles
In cell biology, the nucleus (pl. nuclei; from Latin nucleus
or nuculeus, or kernel), also sometimes referred to as the
"control center", is a membrane-enclosed organelle
found in eukaryotic cells. It contains most of the cell’s
genetic material, organized as multiple long linear DNA
molecules in complex with a large variety of proteins,
such as histones, to form chromosomes. The genes with-
in these chromosomes are the cell’s nuclear genome.
The function of the nucleus is to maintain the integrity
of these genes and to control the activities of the cell by
regulating gene expression - the nucleus is therefore the
control center of the cell.
The main structures making up the nucleus are the
nuclear envelope, a double membrane that encloses the
entire organelle and separates its contents from the cel-
lular cytoplasm, and the nuclear lamina, a meshwork
within the nucleus that adds mechanical support, much
like the cytoskeleton supports the cell as a whole. Be-
cause the nuclear membrane is impermeable to most
molecules, nuclear pores are required to allow move-
ment of molecules across the envelope. These pores
cross both of the membranes, providing a channel that
allows free movement of small molecules and ions. The
movement of larger molecules such as proteins is care-
fully controlled, and requires active transport regulated
by carrier proteins. Nuclear transport is crucial to cell
function, as movement through the pores is required for
both gene expression and chromosomal mainten