Among other organelles such as the endoplasmic reticulum, Golgi apparatus, lysosomes, vacuoles, and the plasma membrane, the nuclear envelope is part of the endomembrane system, involved in the selective transport of molecules within the cell and also with the external environment.
Structure of Nuclear Envelope
When does the Nuclear Envelope Dissolve
Differences in Plant and Animal Cell Nuclear Envelopes
Functions of Nuclear Envelope
Recent research suggests that the nuclear envelope is not a spherical coat. However, the surface cleaves or invaginates, producing channels forming tubules in the nucleoplasm.
What is it Made of
The different parts within the nuclear envelope are:
1. Outer Membrane
It is a double-layered lipid membrane studded with ribosomes participating in protein synthesis. The outer membrane thus separates the cytoplasm from the perinuclear space. It is continuous in many places with the rough endoplasmic reticulum, so the space between the inner and outer nuclear membranes is directly connected with the lumen of the endoplasmic reticulum. The outer membrane contains a large number of proteins.
2. Inner Membrane
It is also made of the lipid bilayer that separates the perinuclear space from the nucleoplasm. The inner membrane is connected to the outer membrane by nuclear pores. It is covered in a nuclear lamina that stabilizes the nuclear envelope, giving the nucleus its shape.
3. Nuclear Pores
A protein-made hole of approximately 120nm in the envelope allows small molecules and ions to diffuse into the nucleus. There are approximately 1000 nuclear pores in a vertebrate cell. Nuclear Pores are also responsible for transporting RNA and proteins from the nucleus into the cytoplasm. The nuclear pores pass through both inner and outer membranes. Small molecules pass through the nuclear pore by passive diffusion. Large molecules are marked by a nuclear localization signal (NLS), a sequence of amino acids that bind to the proteins and function as chaperons through the nuclear pore. Proteins and RNAs are transported out of the nucleus with the help of a nuclear export sequence (NES). Animal cells have centrosomes, structures that help organize DNA when the cell is preparing to divide. In contrast, plants lack these structures and rely entirely on the nuclear membrane for the organization during cell division. Main Function The primary purpose of the envelope is to separate the chromosomes from the cell’s cytoplasm and other contents. It also protects the delicate inner contents of the nucleus, including the DNA. Other Roles
Allows selective entry of small as well as large molecules through the nuclear poresAllows communication between the outer and the inner membraneThe inner membrane with the nuclear lamina gives the structural framework to the nucleus
