Defination of nuclear membrane
Answers
Answer:
A nuclear membrane is a double membrane that encloses the cell nucleus. It serves to separate the chromosomes from the rest of the cell. The nuclear membrane includes an array of small holes or pores that permit the passage of certain materials, such as nucleic acids and proteins, between the nucleus and cytoplasm.
The nuclear envelope, also known as the nuclear membrane,[1][a] is made up of two lipid bilayer membranes that in eukaryotic cells surrounds the nucleus, which encases the genetic material.
Nuclear envelope
Diagram human cell nucleus.svg
Human cell nucleus
Identifiers
TH
H1.00.01.2.01001
FMA
63888
Anatomical terminology
[edit on Wikidata]
The nuclear envelope consists of two lipid bilayer membranes: an inner nuclear membrane and an outer nuclear membrane.[4] The space between the membranes is called the perinuclear space. It is usually about 20–40 nm wide.[5][6] The outer nuclear membrane is continuous with the endoplasmic reticulum membrane.[4] The nuclear envelope has many nuclear pores that allow materials to move between the cytosol and the nucleus.[4] Intermediate filament proteins called lamins form a structure called the nuclear lamina on the inner aspect of the inner nuclear membrane and give structural support to the nucleus.[4]
Structure Edit
The nuclear envelope is made up of two lipid bilayer membranes. An inner nuclear membrane and an outer nuclear membrane. These membranes are connected to each other by nuclear pores. Two sets of intermediate filaments provide support for the nuclear envelope. An internal network forms the nuclear lamina on the inner nuclear membrane.[7] A looser network forms outside to give external support.[4] The actual shape of the nuclear envelope is irregular. It has invaginations and protrusions and can be observed with microscopes that provide sufficient resolution (e.g., electron microscope).[8]
A volumetric surface render (red) of the nuclear envelope of one HeLa cell. The cell was observed in 300 slices of electron microscopy, the nuclear envelope was automatically segmented and rendered. One vertical and one horizontal slice are added for reference.
Outer membrane Edit
The outer nuclear membrane also shares a common border with the endoplasmic reticulum.[9] While it is physically linked, the outer nuclear membrane contains proteins found in far higher concentrations than the endoplasmic reticulum.[10] All four nesprin proteins (nuclear envelope spectrin repeat proteins) present in mammals are expressed in the outer nuclear membrane.[11] Nesprin proteins connect cytoskeletal filaments to the nucleoskeleton.[12] Nesprin-mediated connections to the cytoskeleton contribute to nuclear positioning and to the cell’s mechanosensory function.[13] KASH domain proteins of Nesprin-1 and -2 are part of a LINC complex (linker of nucleoskeleton and cytoskeleton) and can bind directly to cystoskeletal components, such as actin filaments, or can bind to proteins in the perinuclear space.[14][15] Nesprin-3 and-4 may play a role in unloading enormous cargo; Nesprin-3 proteins bind plectin and link the nuclear envelope to cytoplasmic intermediate filaments.[16] Nesprin-4 proteins bind the plus end directed motor kinesin-1.[17] The outer nuclear membrane is also involved in development, as it fuses with the inner nuclear membrane to form nuclear pores.[18]
Inner membrane Edit
Further information: Inner nuclear membrane proteins
The inner nuclear membrane encloses the nucleoplasm, and is covered by the nuclear lamina, a mesh of intermediate filaments which stabilizes the nuclear membrane as well as being involved in chromatin function and entire expression.[10] It is connected to the outer membrane by nuclear pores which penetrate the membranes. While the two membranes and the endoplasmic reticulum are linked, proteins embedded in the membranes tend to stay put rather than dispersing across the continuum.[19] It is lined with a fiber network called the nuclear lamina which is 10-40 nm thick and provides strength.
Mutations in the inner nuclear membrane proteins can cause several nuclear envelopathies.
Nuclear pores Edit
Main article: Nuclear pore
Nuclear pores crossing the nuclear envelope
The nuclear envelope is punctured by thousands of nuclear pores, large hollow protein complexes about 100 nm across, with an inner channel about 40 nm wide.[10] They link the inner and outer nuclear membranes.