The nucleus is a control center found in all eukaryotic cells including those found in animals, plants, protists, and fungi. This is where genetic material, also known as DNA, is kept. A double-layered membrane called the nuclear membrane or nuclear envelope surrounds each nucleus. The nucleoplasm, or fluid inside the nucleus, is separated from the cytoplasm, or fluid outside the nucleus, by this membrane.
A brief note:
Nuclear Membrane Appearance:
There are two membranes that make up the nuclear envelope:
- an outer membrane and
- an inner membrane.
Two layers of phospholipids make up each membrane. This means that there are four rows of phospholipids across the entire nuclear membrane. The perinuclear space separates the inner and outer membranes.
The rough endoplasmic reticulum, an organelle involved in the production and transport of proteins, is connected to the outer nuclear membrane. Ribosomes, which are the actual sites of protein synthesis, are found in both the rough endoplasmic reticulum and the outer nuclear membrane.
The nuclear membrane is a physical barrier that protects the cell’s DNA from chemical reactions occurring elsewhere. If molecules from the cytoplasm enter the nucleus, they may damage part of the cell’s DNA, preventing it from functioning properly and possibly leading to cell death. A network of proteins in the envelope helps to keep the genetic material in place inside the nucleus.
It also controls which materials are allowed to enter and leave the nucleus. It accomplishes this by allowing only certain types of information to pass through. Only a few proteins have the ability to physically pass through the double layer. This keeps genetic information separate from the rest of the cell and allows different cellular activities to take place inside the nucleus and outside the nucleus in the cytoplasm, which houses all other cellular structures.
Nuclear Membrane Components:
The nuclear membrane, like the cell membrane, is a lipid bilayer, consisting of two layers of lipid molecules. Ribosomes, the structures that make proteins, are found on the surface of the lipids’ outer layer. The endoplasmic reticulum, a cell structure that packages and transports proteins, is connected to it.
Proteins in the inner membrane help organize the nucleus and keep genetic material in place. The nuclear lamina is a network of fibers and proteins attached to the inner membrane. It supports the nucleus structurally, assists in DNA repair, and regulates cell cycle events such as cell division and DNA replication. The nuclear lamina is only found in animal cells, though plant cells’ inner membranes may contain some similar proteins.
Nuclear pores pass between the outer and inner membranes of the nuclear membrane. They’re made up of large protein complexes that let specific molecules pass through the nuclear membrane. About 30 different proteins make up each nuclear pore, which works together to transport materials. They also act as connective tissue between the outer and inner membranes.
More nuclear pores are formed in the nuclear membrane during cell division to prepare for cell division. The nuclear membrane eventually breaks down and re-forms around each of the two daughter cells’ nuclei.
The nucleolus is a distinct structure found in the nuclei of eukaryotic cells. It is responsible for the detection of cellular stress, as well as the identification of transfer RNA. It is primarily responsible for ribosome assembly, transfer RNA modification and cellular stress detection. RNA and proteins form the nucleolus, which forms around specific chromosomal regions.
The cell nucleus, the most prominent organelle of the eukaryotic cell, is made up of nucleoplasm, a type of protoplasm. The nuclear envelope, also known as the nuclear membrane, surrounds it. The nucleoplasm is a gel-like substance found within a membrane, similar to the cytoplasm of a eukaryotic cell, but it only fills the space in the nucleus and has its own set of functions.
The nucleoplasm is responsible for maintaining the shape of the nucleus by suspending non-membrane-bound structures within the nucleus. Chromosomes, nuclear bodies, nucleoporins, and nuclear speckles are among the structures suspended in the nucleoplasm.
Karyoplasm, karyolymph, and nucleus sap are all terms for nucleoplasm. The nucleosol, also known as nuclear hyaloplasm, is the soluble, liquid portion of the nucleoplasm.
Heterochromatin is a type of DNA that is tightly packed or condensed and comes in a variety of shapes and sizes. Between the two extremes of constitutive heterochromatin and facultative heterochromatin, these varieties exist on a spectrum. Gene expression is influenced by both of these factors. It was thought that because it is tightly packed, it would be inaccessible to polymerases and thus would not be transcribed.
Euchromatin is a type of chromatin (DNA, RNA, and protein) that is densely packed with genes and is frequently (but not always) active transcription. Heterochromatin, on the other hand, is densely packed and thus less accessible for transcription. The human genome is euchromatic in 92% of cases.
Euchromatin is the most active portion of the genome within the cell nucleus in eukaryotes. Euchromatin is the only type of chromatin found in prokaryotes, implying that heterochromatin evolved later, along with the nucleus, possibly as a mechanism to cope with growing genome sizes.
Ribosomes, also known as Palade granules, are macromolecular machines that perform biological protein synthesis in all cells. Ribosomes link amino acids together in the order specified by messenger RNA molecules’ codons to form polypeptide chains.
Nuclear Membranes in Plant and Animal Cells: What’s the Difference?
Animal and yeast cell nuclear membranes are much better understood than plant cell nuclear membranes, but thanks to recent research, the knowledge gap is closing. Plant nuclear membranes lack many of the proteins found on animal cell nuclear membranes, but they do have some pore membrane proteins that are only found in plants. Animal cells have centrosomes, which help organize DNA as the cell prepares to divide; plants, on the other hand, lack these structures and appear to rely solely on the nuclear membrane for cell division organization. Scientists may be able to better understand the uniqueness of plant cell nuclear membranes with more research.
Importance of chapter for NEET and Board Exams:
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This article on ‘how to prepare for NEET and Class 12 board exams at the same time aims to assist candidates in preparing for both exams at the same time. The NEET 2022 exam is scheduled to take place in the first week of May, while the CBSE Class 12 board exam will begin in February/March.
Also read: Nucleolus
1. How are nucleus and nuclear membranes interconnected?
Soln.: Nuclear pores, large protein complexes that regulate molecular traffic into and out of the nucleus, connect the two nuclear membranes. Proteins with nuclear localization signals that are synthesized in the cytosol bind to the nuclear pore and are actively transported into the nucleus.
2. What distinguishes the nuclear membrane from other membranes?
Soln.: The lipid bilayer that surrounds the entire cell is known as the cell membrane. The nuclear membrane, on the other hand, surrounds the nucleus. The cell membrane is made up of a continuous sheet of material.
3. What is the nuclear membrane made of?
Soln.: Two phospholipid bilayers make up the nuclear membrane. The outer nuclear membrane (ONM) faces the cytoplasm, while the inner nuclear membrane (INM) faces the nucleoplasm.
4. How did the nuclear membrane form?
Soln.: The binding of vesicles formed during nuclear membrane breakdown to the surface of chromosomes is the first step in the re-formation of the nuclear envelope. Both lamins and integral membrane proteins of the inner nuclear membrane may be involved in the interaction of membrane vesicles with chromosomes. The vesicles then join together to form a double membrane that encases the chromosomes. The nuclear pore complexes are then reassembled, the nuclear lamina is reformed, and the chromosomes are decondensed. The vesicles first fuse together to form membranes around individual chromosomes, which then fuse together to form a single nucleus.