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 membrane. When we divide the organisms that live on this planet, we make a distinction between those that have a nucleus, that are called eukaryotes, and those that don't have a nuclei, which we call prokaryotes.
The nucleus contains all of the genetic material for a eukaryotic cell, but this genetic material needs to be protected. Furthermore, the main function of the nuclear membrane is to make a distinct biochemical environment inside the nucleus. Only small, nonpolar molecules can move across the nuclear membrane. The nuclear envelope is the covering of the nucleus, which is made up of the nuclear membrane.
It contains nuclear pores through which a selective traffic of RNA and protein molecules occur. Therefore, the main function of the nuclear pores is to regulate eukaryotic gene expression. Thus, the nuclear pore complex is the only path that allows the movement of macromolecules, ions as well as small polar molecules across the nuclear envelope.
Figure 2: Nuclear Envelope. The nuclear pore complex is comparatively large and its diameter is around nm, which is thirty times larger than a ribosome. Here, small proteins whose size is less than 50 kDa can move freely in either direction through the nuclear pore complex. However, most proteins and RNAs move across the nuclear pore complex by using an active mechanism, which recognizes and transports appropriate proteins to appropriate directions. Nuclear membrane refers to a double membrane enclosing a cell nucleus and having its outer part continuous with the endoplasmic reticulum.
Nuclear envelope refers to a double membrane structure that surrounds the nucleus in eukaryotic cells and provides this compartmentalization. The inner membrane is constituted by a network of filaments called nuclear lamina. The lamina attach to chromosomes. It also acts like a shield for the nucleus. The outer and the inner membranes are connected by the nuclear pores. In mammals, the nuclear envelope spectrin repeat proteins are expressed in the outer membrane. These proteins connect the cytoskeleton s in the cytoplasm to the nucleoskeleton in the nucleoplasm.
This connection aids in the positioning of the nucleus within the cell. During cell division, the nuclear envelope undergoes major changes in animal and plant cells. The nuclear envelope disintegrates to allow the spindle fibers to access the chromosomes in the nucleus. An exception to this is the yeast cells whereby the nuclear envelope stays intact during cell division.
In animal and plant cells, the nuclear envelope breaks down into pieces during prometaphase of mitosis. Then, during telophase, the nuclear membrane reforms.
The reformation process remains unclear how it proceeds. It is postulated to occur via vesicle fusion or probably by reshaping of the endoplasmic reticulum, enclosing the nuclear region with a new nuclear envelope. The presence of the nuclear envelope prevents the easy passage of large molecules e.
Although the nuclear envelope is perforated with nuclear pores, large molecules would still need a nuclear transport mechanism in order to enter and exit the nucleus. Small molecules, such as ions, can pass through the nucleus with ease. However, cargo proteins and RNAs that need to be transported require importins and exportins to enter and exit the nucleus, respectively.
On one hand, the cargo binds with the importin in the cytoplasm, and then moved into the nucleus through the nuclear pore.
0コメント