Everything about The Nuclear Envelope totally explained
The
nuclear envelope (also known as the
perinuclear envelope,
nuclear membrane,
nucleolemma or
karyotheca) is the double
membrane of the
nucleus that encloses genetic material in
eukaryotic cells. It separates the contents of the nucleus (
DNA in particular) from the
cytosol (cytoplasm).
Numerous
nuclear pores are present on the nuclear envelope to facilitate and regulate the exchange of materials (for example,
proteins and
RNA) between the nucleus and the cytoplasm.
The space between the two membranes that make up the nuclear envelope is called the perinuclear space (also called the perinuclear cisterna), and is usually about 20 - 40 nm wide. Each of the two membranes is composed of a
lipid bilayer. The outer membrane is continuous with the
rough endoplasmic reticulum.
The inner membrane is erected upon the
nuclear lamina, a network of
intermediate filaments made of
lamin, that plays a role in
mitosis and
meiosis. The type of lamins present are A, B1, B2, and C.
The nuclear envelope may also play a role in the disposition of
chromatin inside the nucleus. The lamina acts as a site of attachment for chromosomes. It also acts like a shield for the nucleus.
Disintegration during mitosis in metazoans
During
prophase in
mitosis, the
chromatids begin condensing to form
chromosomes, and the nuclear envelope begins to disintegrate. During
metaphase, the nuclear envelope is completely disintegrated, and the chromosomes can be pulled apart as chromatids by the
spindle fibers. Other eukaryotes such as yeast undergo closed mitosis, where the chromosomes segregate within the nuclear envelope, which then buds as the two daughter cells divide.
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