What is the Difference Between Nuclear Membrane and Nuclear Envelope

The main difference between nuclear membrane and nuclear envelope is that the nuclear membrane is the selective barrier between the nucleoplasm and cytoplasm whereas the nuclear envelope is the structure that separates the content of the nucleus from the cytoplasm. Furthermore, nuclear membrane is a lipid bilayer while nuclear envelope consists of two nuclear membranes and nuclear pores. 

Nuclear membrane and nuclear envelope are two structural components of the nucleus in all eukaryotic cells with a nucleus.

Key Areas Covered 

1. What is Nuclear Membrane
     – Definition, Components, Role
2. What is Nuclear Envelope
     – Definition, Structure, Role
3. What are the Similarities Between Nuclear Membrane and Nuclear Envelope
     – Outline of Common Features
4. What is the Difference Between Nuclear Membrane and Nuclear Envelope
     – Comparison of Key Differences

Key Terms 

Lipid Bilayer, Nuclear Envelope, Nuclear Membrane, Nuclear Pore Complex, Nucleus, Selective Transport 

What is Nuclear Membrane 

The nuclear membrane is the lipid bilayer which surrounds the nucleoplasm from the cytoplasm. The two layers of the nuclear membrane are the inner nuclear membrane and the outer nuclear membrane. Perinuclear space, which is around 20-40 nm wide, refers to the space between the two layers. Moreover, nuclear lamina occurs internally to the inner nuclear membrane. It is made up of intermediate filaments. These filaments also occur in the outer surface of the outer nuclear membrane, providing structural support to the contents of the nucleus. In addition, the outer nuclear membrane is continuous with the endoplasmic reticulum.  

Figure 1: Nuclear Membrane

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.  

What is Nuclear Envelope 

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 120 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.  

Similarities Between Nuclear Membrane and Nuclear Envelope 

• Nuclear membrane and nuclear envelope are two structural components of the nucleus in all eukaryotic cells with a nucleus. 
• Both surround the content of the nucleus from the cytoplasm. 
• Moreover, they serve as a selective barrier by allowing the transport of selected materials across them. 
• Therefore, they help to maintain a unique environment inside the nucleus. 

Difference Between Nuclear Membrane and Nuclear Envelope 

Definition 

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. These definitions explain the main difference between nuclear membrane and nuclear envelope.

Structure 

Another difference between nuclear membrane and nuclear envelope is that the nuclear membrane consists of a lipid bilayer while the nuclear envelope consists of the nuclear membrane with nuclear pores. 

Role 

Respective functions are an important difference between nuclear membrane and nuclear envelope. The nuclear membrane serves as a selective barrier for the transport of materials across it while nuclear envelope surrounds the content of the nucleus from the cytoplasm.

Conclusion 

The nuclear membrane is the lipid bilayer which serves as a selective barrier to the movement of materials across it. The nuclear envelope, on the other hand, is the membrane system of the nucleus, which separates the content of the nucleus from the cytoplasm. Therefore, the main difference between nuclear membrane and nuclear envelope is their structure and role.

Reference:

1. Cooper GM. The Cell: A Molecular Approach. 2nd edition. Sunderland (MA): Sinauer Associates; 2000. The Nuclear Envelope and Traffic between the Nucleus and Cytoplasm. Available Here

Image Courtesy:

1. “Nuclear membrane” By Boumphreyfr – Own work (CC BY-SA 3.0) via Commons Wikimedia  
2. “0318 Nucleus” By OpenStax –  (CC BY 4.0) via Commons Wikimedia