The outer and inner nuclear membrane are fused at the site of nuclear pore. Chacha on!
A nuclear membrane, also known as the nuclear envelope, nucleolemma or karyotheca, is the double lipid bilayer membrane which surrounds the genetic material and nucleolus in eukaryotic cells.
The nuclear membrane consists of two lipid bilayers—the inner nuclear membrane, and the outer nuclear membrane. The space between the membranes is called the perinuclear space, a region contiguous with the lumen (inside) of the endoplasmic reticulum. It is usually about 20–40 nm wide.
Nuclear pores are large protein complexes that cross the nuclear envelope, which is the double membrane surrounding the eukaryotic cell nucleus. There are about an average of 2000 nuclear pore complexes (NPCs), in the nuclear envelope of a vertebrate cell, but it varies depending on cell type and the stage in the life cycle. The proteins that make up the nuclear pore complex are known as nucleoporins. About half of the nucleoporins typically contain either an alpha solenoid or a beta-propeller fold, or in some cases both as separate structural domains. Each NPC contains at least 456 individual protein molecules and is composed of 30 distinct proteins (nucleoporins). The other half show structural characteristics typical of "natively unfolded" or intrinsically disordered proteins, i.e. they are highly flexible proteins that lack ordered secondary structure. These disordered proteins are the FG nucleoporins, so called because their amino-acid sequence contains many repeats of the peptide phenylalanine—glycine.
Nuclear pore complexes allow the transport of molecules across the nuclear envelope. This transport includes RNA and ribosomal proteins moving from nucleus to the cytoplasm and proteins (such as DNA polymerase and lamins), carbohydrates, signaling molecules and lipids moving into the nucleus. It is notable that the nuclear pore complex (NPC) can actively conduct 1000 translocations per complex per second. Although smaller molecules simply diffuse through the pores, larger molecules may be recognized by specific signal sequences and then be diffused with the help of nucleoporins into or out of the nucleus. This is not directly energy requiring, but depends on concentrations gradients associated with the RAN cycle. Each of the eight protein subunits surrounding the actual pore (the outer ring) projects a spoke-shaped protein over the pore channel. The center of the pore often appears to contain a plug-like structure. It is yet unknown whether this corresponds to an actual plug or is merely cargo caught in transit.
In cell biology, the nucleus (pl. nuclei; from Latin nucleus or nuculeus, meaning kernel) 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 within 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 isolates its contents from the cellular cytoplasm, and the nucleoskeleton (which includes nuclear lamina), a network within the nucleus that adds mechanical support, much like the cytoskeleton, which supports the cell as a whole. Movement of large molecules such as proteins and RNA through the pores is required for both gene expression and the maintenance of chromosomes. Because the nuclear membrane is impermeable to large molecules, nuclear pores are required that regulate nuclear transport of molecules across the envelope. The pores cross both nuclear membranes, providing a channel through which larger molecules must be actively transported by carrier proteins while allowing free movement of small molecules and ions. The interior of the nucleus does not contain any membrane-bound sub compartments, its contents are not uniform, and a number of sub-nuclear bodies exist, made up of unique proteins, RNA molecules, and particular parts of the chromosomes. The best-known of these is the nucleolus, which is mainly involved in the assembly of ribosomes. After being produced in the nucleolus, ribosomes are exported to the cytoplasm where they translate mRNA.
A biological membrane or biomembrane is an enclosing or separating membrane that acts as a selectively permeable barrier, within or around a cell. It consists of a phospholipid bilayer with embedded , integral and peripheral proteins used in communication and transportation of chemicals and ions. The cellular membranes should not be confused with isolating tissues formed by layers of cells, such as mucous and basement membranes.
The inner membrane is the biological membrane (phospholipid bilayer) of an organelle or Gram-negative bacteria that is within an outer membrane.
In eukaryotic cells, this inner membrane is present within the nuclear envelope, mitochondria and plastids like the chloroplast. The lumen between the inner and outer membranes is referred to as intermembrane space.
The endomembrane system is composed of the different membranes that are suspended in the cytoplasm within a eukaryotic cell. These membranes divide the cell into functional and structural compartments, or organelles. In eukaryotes the organelles of the endomembrane system include: the nuclear envelope, the endoplasmic reticulum, the Golgi apparatus, lysosomes, vacuoles, vesicles, endosomes and the cell membrane. The system is defined more accurately as the set of membranes that form a single functional and developmental unit, either being connected directly, or exchanging material through vesicle transport. Importantly, the endomembrane system does not include the membranes of mitochondria and chloroplasts.
The nuclear envelope is a membrane containing two layers, that encompasses the contents of the nucleus. The endoplasmic reticulum (ER) is a synthesis and transport organelle that branches into the cytoplasm in plant and animal cells. The Golgi apparatus is a series of multiple compartments where molecules are packaged for delivery to other cell components or for secretion from the cell. Vacuoles, which are found in both plant and animal cells (though much bigger in plant cells), are responsible for maintaining the shape and structure of the cell as well as storing waste products. A vesicle is a relatively small, membrane-enclosed sac that stores or transports substances. The plasma membrane, also referred to as the cell membrane, is a protective barrier that regulates what enters and leaves the cell. There is also an organelle known as the spitzenkörper that is only found in fungi, and is connected with hyphal tip growth.
Cell biology (formerly cytology, from the Greek kytos, "contain") is a scientific discipline that studies cells – their physiological properties, their structure, the organelles they contain, interactions with their environment, their life cycle, division and death. This is done both on a microscopic and molecular level. Cell biology research encompasses both the great diversity of single-celled organisms like bacteria and protozoa, as well as the many specialized cells in multicellular organisms such as humans, plants, and sponges.
Knowing the components of cells and how cells work is fundamental to all biological sciences. Appreciating the similarities and differences between cell types is particularly important to the fields of cell and molecular biology as well as to biomedical fields such as cancer research and developmental biology. These fundamental similarities and differences provide a unifying theme, sometimes allowing the principles learned from studying one cell type to be extrapolated and generalized to other cell types. Therefore, research in cell biology is closely related to genetics, biochemistry, molecular biology, immunology, and developmental biology.
Membrane biology is the study of the biological and physiochemical characteristics of membranes.