Cell nucleus

The cell nucleus is a <a href="/facts/Membrane-bound_organelle/vhDFnGbs">membrane-bound organelle</a> found in <a href="/facts/Eukaryote/SkwyPLMA">eukaryotic</a> <a href="/facts/Cell_(biology)/bLM9UQvy">cells</a>. Eukaryotic cells usually have a single nucleus, but a few cell types, such as mammalian <a href="/facts/Red_blood_cell/Kggpq8Jh">red blood cells</a>, have no nuclei, and a few others including <a href="/facts/Osteoclast/jHHtEQru">osteoclasts</a> have <a href="/facts/Multinucleate/mvaHLA0V">many</a>. The main structures making up the nucleus are the <a href="/facts/Nuclear_envelope/IwRQ5BVL">nuclear envelope</a>, a double membrane that encloses the entire organelle and isolates its contents from the cellular <a href="/facts/Cytoplasm/Wa0sE6xf">cytoplasm</a>; and the <a href="/facts/Nuclear_matrix/cAEsB6nd">nuclear matrix</a>, a network within the nucleus that adds mechanical support.
The cell nucleus contains nearly all of the cell's <a href="/facts/Genome/31Sm08JT">genome</a>. <a href="/facts/Nuclear_DNA/5wzCJQlb">Nuclear DNA</a> is often organized into multiple <a href="/facts/Chromosome/FRGf11FC">chromosomes</a> – long strands of <a href="/facts/DNA/nB89Iauz">DNA</a> dotted with various <a href="/facts/Protein/Jxmagu3E">proteins</a>, such as <a href="/facts/Histone/krb5VJfp">histones</a>, that protect and organize the DNA. The <a href="/facts/Gene/e1swwPY6">genes</a> within these chromosomes are <a href="/facts/Nuclear_organization/jf5CngSq">structured</a> in such a way to promote cell function. The nucleus maintains the integrity of genes and controls the activities of the cell by regulating <a href="/facts/Gene_expression/alCPohLR">gene expression</a>.
Because the nuclear envelope is impermeable to <a href="/facts/Macromolecule/039ULSLg">large molecules</a>, <a href="/facts/Nuclear_pore/CQ4IQG4s">nuclear pores</a> are required to regulate <a href="/facts/Nuclear_transport/gfacmN4N">nuclear transport</a> of molecules across the envelope. The pores cross both nuclear membranes, providing a <a href="/facts/Ion_channel/A46LARFH">channel</a> through which larger molecules must be <a href="/facts/Active_transport/7EAcsfb2">actively transported</a> by carrier proteins while allowing free movement of small molecules and <a href="/facts/Ion/3bePpDna">ions</a>. Movement of large molecules such as proteins and <a href="/facts/RNA/HxPeNfNj">RNA</a> through the pores is required for both gene expression and the maintenance of chromosomes. Although the interior of the nucleus does not contain any membrane-bound subcompartments, a number of <a href="/facts/Nuclear_bodies/rASoQI7z">nuclear bodies</a> exist, made up of unique proteins, RNA molecules, and particular parts of the chromosomes. The best-known of these is the <a href="/facts/Nucleolus/X7B5HKM4">nucleolus</a>, involved in the assembly of <a href="/facts/Ribosome/CF2u2gtg">ribosomes</a>.

Cell nucleus open-in-new

Cell nucleus