Nuclear Membrane – Function, Structure, and Diagram

The nuclear membrane is a double-layered structure surrounding the nucleus in eukaryotic cells. It serves as a protective barrier and consists of an outer and inner lipid bilayer. The nuclear membrane regulates the passage of molecules in and out of the nucleus. The nuclear membrane is absent in prokaryotes. In this article, we will learn about the parts and functions of the nuclear membrane and more.

What is Nuclear Membrane?

The nuclear membrane is also known as the nuclear envelope. It is a double membrane structure that surrounds the nucleus of eukaryotic cells and separates the contents of the nucleus from the cytoplasm of the cell. The inner and the outer membranes are separated by a space called the perinuclear space.

The nuclear membrane controls the movement of molecules between the nucleus and cytoplasm. It also supports the nucleus, regulates gene expression, and connects with the endoplasmic reticulum. It is a dynamic structure and undergoes continuous rearrangements carrying out various nuclear functions.

Nuclear Membrane Structure

The nuclear membrane contains 4 major parts:

• Inner Nuclear Membrane: This is the innermost layer of the nuclear envelope, facing the nucleoplasm. It is associated with proteins and structures involved in chromatin organization and gene regulation.
• Outer Nuclear Membrane: This is the outer nuclear membrane which faces the cytoplasm. It is continuous with the endoplasmic reticulum and contains proteins and structures involved in maintaining the structural integrity of the nucleus. It facilitates communication between the nucleus and the cytoplasm.
• Perinuclear Space: This is the space between the inner and outer nuclear membranes. It provides a buffer zone and allows for the movement of molecules between the two membranes.
• Nuclear Pore Complexes: These are protein complexes embedded in the nuclear membrane. They facilitate the regulated exchange of molecules such as RNA and proteins between the nucleus and the cytoplasm and hence are responsible for the movement of molecules in and out of the nucleus.

Nuclear Membrane Diagram

The labelled diagram of nuclear membrane is shown below:

Diagram of Nuclear Membrane

Breakdown and Formation of the Nuclear Membrane

During cell division, the nuclear membrane breaks down, allowing the chromosomes to separate, and subsequently reforms around the newly formed nuclei in daughter cells.

Break Down

The nuclear membrane break down begins at the beginning of prophase and continues till prometaphase. This disintegration allows the spindle apparatus to capture the condensed chromosomes. The nuclear membrane disintegration occurs by the phosphorylation of the nuclear pore proteins and break down of the nuclear lamina.

Reformation

Nuclear envelope reformation starts during the anaphase and lasts into the G1 phase of the cell cycle in species with open mitosis. At the end of anapahase or in early telophase, the nuclear membrane starts to reassemble around the separated sets of chromosomes. This process involves the dephosphorylation of nuclear pore proteins and the reformation of nuclear pores. The nuclear envelope precursors, which are derived from the endoplasmic reticulum (ER) membranes, begin to enclose the chromatin.

Functions of the Nuclear Membrane

The nuclear membrane contains the nuclear contents and hosts a variety of processes within it. The functions of the nuclear membrane are:

• The nuclear membrane function as a wall dividing the cytoplasm from the contents of the nucleus.
• The nuclear membranes are phospholipid bilayers, much like other cell membranes, and they are selectively permeable, i.e,. they only allow tiny, nonpolar molecules to pass through. The phospholipid bilayer prevents the diffusion of other chemicals.
• The nuclear pore complex allows certain proteins and RNAs to go back and forth between the cytoplasm and the nucleus.
• The nuclear lamina, a fibrous meshwork that supports the nucleus structurally, lies underneath the inner nuclear membrane. One or more similar proteins known as lamins make up the nuclear lamina.

Importance of the Nuclear membrane

The nuclear membrane holds immense significance as it has diversified functions in controling the cell functioning and accomodating the genetic material.

• It is a protective shield that prevents any damage to the enclosed DNA.
• It acts a barrier and controls the molecular inflow and outflow.
• It plays an important role in cell signalling and gene expression because it is the part that senses the cytoplasmic signals brought to the nucleus.
• It also maintains the chromatin structure by anchoring it to the lamina.

Difference Between Plasma and Nuclear Membrane

The nuclear membrane and the plasma membrane based on the following criteria:

Nuclear Membrane	Plasma Membrane
The nuclear membrane is a double membrane.	The plasma membrane is a single membrane.
It is discontinuous and has intricate holes.	It is continuous and pore less.
Nuclear membrane has two concentric phospholipid bilayers.	The plasma membrane has just one concentric phospholipid bilayer.
The nuclear membrane shields the cell’s DNA and divides the nucleus from the cytoplasm.	The plasma membrane shields the cell from outside stresses and divides its inside components from its outside.

Difference Between Plant and Animal Nuclear Membrane

The difference between Plant and Animal Nuclear membrane is Summarised below:

Plant Nuclear Membrane	Animal Nuclear Membrane
Lamin proteins or their homologues have not been reported in plant nuclear membrane.	The inner nuclear membrane of an animal cell is firmly covered with a protein structure called the nuclear lamina
Centrosomes are absent	Centrosomes are present that aid in spindle formation during mitosis.

Diseases Caused by the Defects in Nuclear Membrane

Disorders of the nuclear membrane include:

• Dilated cardiomyopathy with variable muscular dystrophy: Caused due to the mutations in the LMNA gene, encoding lamin A/C proteins that are important for maintaining the structure and function of the nuclear envelope. It is characterised by progressive muscle weakness and wasting, particularly in the shoulders, upper arms, and calves. It is often accompanied by cardiac abnormalities such as dilated cardiomyopathy
• Dunnigan-type familial partial lipodystrophy: Also caused by the mutations in the LMNA gene affecting nuclear envelope function. Selective loss of fat tissue, particularly in the limbs and trunk, leading to abnormal fat distribution and metabolic complications such as insulin resistance, diabetes, and dyslipidemia can be observed. Progressive muscle weakness and wasting, particularly in the feet and lower legs, resulting in difficulties with walking and balance.
• Charcot-Marie-Tooth type 2 disease: CMT2 can have various genetic causes, one such mutation in the gene LMNA can result in abnormal nuclear envelope function.
• Mandibuloacral dysplasia: Mutations in the LMNA or ZMPSTE24 genes, both of which are involved in nuclear envelope structure and function, have been associated with this disorder.
• Hutchinson-Gilford progeria syndrome: HGPS is caused by a mutation in the LMNA gene, resulting in the production of a truncated, abnormal form of lamin A protein called progerin, which disrupts nuclear envelope function and cellular processes.

Conclusion – Nuclear Membrane

The nuclear membrane is a double layer that encloses the cell’s nucleus, where the chromosomes reside. The chromosomes are separated from the cytoplasm and other cellular components by the nuclear membrane. The nuclear membrane is essentially made of two concentric lipid bilayers. The endoplasmic reticulum (ER) and the outer lipid bilayer are continuous, making up the two concentric lipid bilayers. Nuclear pore complexes act as pathways for molecular exchanges between the cytoplasm and nucleus. The nuclear membranes’ essential job is to operate as a wall dividing the cytoplasm from the contents of the nucleus. The nuclear membranes are phospholipid bilayers, much like other cell membranes, and they are selectively permeable.

FAQs on Nuclear Membrane

What is a Nuclear Membrane Made of?

The nuclear membrane is essentially made of two concentric lipid bi layers, inner and outer membranes. It also consists of nuclear lamins and a nuclear pore complex. The nuclear lamina is a layer made up of A and B type of lamins.

How Does the Nuclear Membrane Appear Like?

The nuclear membrane appears to be a spherical compartment in an eukaryotic cell. It contains the chromatin network and a prominent darkly stained nucleolus. In plant cells, it may be pushed to the side due to the vacuole.

Why Does the Nuclear Envelope Break During Mitosis?

The nuclear membrane disintegrates during mitosis, specifically in the prophase to facilitate spindle fibre formation. The disintegration of the envelope also allows segregation of chromosomes.

What Would Happen if the Nucleus Had no Membrane?

In the absence of a nuclear membrane, important cellular genetic functions and their regulation doesn’t happen. This leads to errors in cellular processes, and finally cell death.

What is a Nuclear Membrane Class 9?

The nuclear membrane is a double-layered membrane that surrounds the nucleus of a cell, acting as a barrier to regulate the passage of molecules in and out of the nucleus.