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Nuclear Envelope: Definition, Function & Structure

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Instructor: Katy Metzler

Katy teaches biology at the college level and did her Ph.D. work on infectious diseases and immunology.

The nuclei of eukaryotic cells are separated from the cytosol by the nuclear envelope. In this lesson, we explore the structure of the nuclear envelope and the functions it performs in cells.

We also recommend watching Structure of the Nucleus: Nucleolus, Nuclear Membrane, and Nuclear Pores and Nuclear vs. Extended Family: Definitions & Structures

Definition

A major hallmark of eukaryotic cells is that they store their genetic material in the nucleus, a compartment that is separate from the cytosol. The nuclear envelope is the double membrane structure that surrounds the nucleus in eukaryotic cells and provides this compartmentalization.

Structure and Functions of the Nuclear Envelope

Below is a diagram of the nuclear envelope. In most cells, the nucleus is sphere-shaped, and this diagram shows a cross-section.

A diagram of the nuclear envelope.

We'll go through each structural component of the nuclear envelope here, and learn about their functions at the same time.

Inner and Outer Nuclear Membranes

The nuclear envelope is made up of a double membrane structure that provides a barrier between the nuclear contents and the cytosol. The inner nuclear membrane and outer nuclear membrane are labeled in the diagram above. The two membranes are connected together, but their protein compositions are different.

Inner Nuclear Membrane

The inner nuclear membrane contains integral and peripheral membrane proteins that anchor the nuclear envelope to the lamina, which is a sturdy protein meshwork that gives the nucleus its structure and shape.

Outer Nuclear Membrane

As you can see in the diagram, the outer nuclear membrane is contiguous with the endoplasmic reticulum (ER), the intracellular compartment where lipids, as well as proteins that are going to be secreted or inserted into membranes, are made. The ER and outer nuclear membrane are both studded with ribosomes, which are the enzymes that translate mRNAs into proteins. The ribosomes are there so that ER proteins can be transported through the ER membrane as they are translated.

Perinuclear Space

The space between the inner and outer nuclear membranes is called the perinuclear space. As shown in the diagram, it is contiguous with the inside of the ER, so the same processes occur in the ER as in the perinuclear space.

Nuclear Pore Complexes

Although the nucleus is a separate compartment from the cytosol, many molecules have to go in and out. These molecules include histones, DNA and RNA polymerases, transcription factors, and ribosomal proteins. They are transported into and out of the nucleus through the nuclear pores, which are large protein complexes that penetrate through both membranes of the nuclear envelope.

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