Cell nucleus : The genetic material cell

In Biology the cell nucleus (from Latin or nuculeus nucleus, the heart of a fruit) is an organelle membranes that are found in the cell eukaryotes . It contains most of the genetic material cell, arranged in multiple linear molecules of DNA very long forming complexes with a variety of proteins such as histones to form chromosomes . The set of genes of these chromosomes are the nuclear genome . The kernel function is to maintain the integrity of these genes and to control cellular activities regulating gene expression . Thus it is said that the nucleus is the control center of the cell.

The main structures that constitute the core are the nuclear envelope , a double membrane completely surrounding the organelle and separates its contents in the cytoplasm , and nuclear lamina , a frame below it that provides mechanical support in a similar way to how the cytoskeleton supports the rest of the cell. Since the nuclear envelope is impermeable to most molecules , the nuclear pores , which cross the two membranes that form, are necessary to allow passage of molecules through it, because they allow the transit of small molecules, such as the ions , but the movement of larger molecules such as proteins is carefully controlled, requiring active transport regulated by transport proteins. The cellular transport is crucial for cell function, since it requires the passage through these pores to gene expression and maintaining chromosome .

Although the nucleus contains no membranous subcompartments, their content is not uniform, and there are a number of subnuclear bodies composed of unique types of proteins, molecules of RNA and specific segments of chromosomes. The best known of these is the nucleolus , which mainly is involved in the synthesis of ribosomes . After being produced in the nucleolus, they are exported to the cytoplasm, where they translate the RNA .

Housing and nuclear pores:

The nuclear envelope , also known as nuclear membrane is composed of two membranes , one internal and one external, arranged in parallel one above the other with a separation of 10-50 nanometers (nm). The nuclear envelope completely surrounding the nucleus and separates the cell’s genetic material surrounding cytoplasm, serving as a barrier that prevents macromolecules spread freely between the nucleoplasm and cytoplasm.  The outer nuclear membrane is continuous with the membrane of rough endoplasmic reticulum (RER), and is also studded with ribosomes .  The space between the membranes and known as perinuclear space is continuous with the light of the RER.
The nuclear pores , which provide aqueous channels that traverse the envelope, consists of multiple proteins collectively known as nucleoporins. The pores are 125 million daltons molecular weight and consist of approximately
50 (in yeast ) to 100 proteins (in vertebrates ). [5] The pores have a diameter of 100 nm, however, the hole through
which broadcast free molecules is 9 nm in width due to the presence of regulatory systems in the center of the pore.

This size allows free passage of small soluble molecules while preventing larger molecules from entering or leaving
an inappropriate manner, such as nucleic acids and large proteins. These large molecules, instead, must be
transported actively to the nucleus. The core of a typical mammalian cell has between 3000 and 4000 pores throughout its envelope, each of which contains a ring structure with octal symmetry in the position in which the membranes, internal and external are merged.  Anchored to the ring is the structure called nuclear basket that extends into the nucleoplasm, and a series of filamentous extensions that project into the cytoplasm.  Both structures measured the protein binding of nuclear transport.

Most proteins, ribosomal subunits and some RNAs are transported through the pore complex in a process mediated by a family of transport factors known as karyopherins . These include the importins , involved in transport towards the
nucleus, and those for the carriage in the opposite direction, known as exportin . Most karyopherins interact directly with their cargo, although some use adapter proteins.  The steroid hormones such as cortisol and aldosterone , as well as other soluble small molecules involved in cell signaling can diffuse through the cell membrane and in the cytoplasm, where they attach to proteins that act as nuclear receptors that are driven to the nucleus.  Serve as transcription factors when bound to its ligand .  In the absence of ligand many such receptors function as histone deacetylases that repress gene expression.