Nuclear Envelope

The nuclear envelope (NE) is a highly complex and regulated membrane barrier that separates the nucleus from the cytoplasm in eukaryotic cells. It is composed of a large number of different proteins that have been implied in chromatin organization and gene regulation. However the nuclear membrane allows complex levels of gene expression, it also constitutes a challenge whenever it comes to cell division. To allow the ingress of the mitotic spindle to chromatin, the nucleus of metazoans should completely disassemble during mitosis, creating the need to re-establish the nuclear chamber at the end of each cell division. The Nuclear Envelope, is the characteristics of eukaryotic cells, it is a highly organized double membrane bound structure that encompasses the nuclear genome. The nuclear envelope, also referred to as the nuclear membrane, is made up of two distinct lipid bilayer membranes that in eukaryotic cells surround the nucleus, which encloses the genetic material.

Function of the Nuclear Membrane

The nuclear membrane functions as a barrier that structurally prevents the cell’s DNA from any chemical reactions that are occurring elsewhere in the cell. If molecules that are present in the cytoplasm were allowed to enter the nucleus, then they can destroy a part of the cell’s DNA, which will further stop it from functioning properly and may even lead to cell death. The envelope also comprises a network of proteins that keeps the genetic material in place inside the nucleus. Nuclear envelope functions to manage what materials can enter and exit the nucleus. It does so as it is   selectively permeable. Only certain specific proteins are able to physically pass through the double layer. This protects genetic information from mixing with other parts of the cell, and further allows different cellular activities that occur inside the nucleus and outside the nucleus in the cytoplasm, in which all other cellular structures are also located.

Parts of the Nuclear Membrane

The nuclear membrane covers the nucleus of the cell, it is comprised of certain specific parts that are discussed below:

Outer Membrane

Similar to the cell membrane, the nuclear membrane is also made up of lipid bilayer, which means that it comprises two layers of lipid molecules. The outer layer of lipids comprises ribosomes, structures that make proteins, on its surface. It is connected to the endoplasmic reticulum, it is a cell structure that helps in packaging and transporting proteins.

Inner Membrane

The inner membrane is made up of proteins that functions to organize the nucleus and allows the accumulation of genetic material in place. This network of fibers and proteins are joined with the inner membrane and are called the nuclear lamina. It supports the nucleus physically, and plays an important role in repairing DNA, and regulating events in the cell cycle like those of cell division and the replication of DNA. The nuclear lamina is only present in animal cells, however plant cells might possess some similar proteins on the inner membrane.

Nuclear Pores

Nuclear pores pass through both the outer and inner membranes of the nuclear membrane. They are composed of large complexes of proteins and allow only certain specific molecules to pass through the nuclear membrane. Each nuclear pore is generally composed of about 30 different proteins that work together to transport materials. They also attach the outer and inner membranes. At the time of cell division, more nuclear pores are being formed on the nuclear membrane in preparation for cell division. The nuclear membrane gradually breaks down and is reformed around the nuclei of each of the two daughter cells.

Nucleolus

These are tiny spherical bodies that are located in the nucleus as they are usually present in a centralized site but are mainly found closer to the nuclear membrane. The nucleolus is known to store the genes that are necessary for full ribosomal production. They help in encoding ribosomal RNA subunits.  

Nucleoplasm

Nucleoplasm is a viscous liquid that comprises the nuclear hyaloplasm which is the more soluble and liquid portion of the nucleoplasm. This type of protoplasm is quite similar to the cytoplasm, which is present throughout the cell body to the exterior of the nucleus. Some of its functions are carried out inside the nucleus, for which a different type of protoplasm is required. The composition of the nucleoplasm is water, dissolved ions, and a mixture of other substances. The nucleoplasm is entirely confined in the nuclear envelope containing nucleotides and other important enzymes that promote replication.

Conclusion

The nuclear envelope is a double membrane made up of an outer and an inner phospholipid bilayer. The thin space present between the two layers attaches with the lumen of the rough endoplasmic reticulum (RER), and the outer layer is an extended portion of the outer face of the RER. Here we come to an end of this topic. We hope that you were able to grasp a clear concept of the topic.