Nuclear Membrane Function & Structure | What is a Nuclear Membrane?

Amanda Robb, Angela Lynn Swafford
  • Author
    Amanda Robb

    Amanda has taught high school science for over 10 years. She has a Master's Degree in Cellular and Molecular Physiology from Tufts Medical School and a Master's of Teaching from Simmons College. She is also certified in secondary special education, biology, and physics in Massachusetts.

  • Instructor
    Angela Lynn Swafford

    Lynn has a BS and MS in biology and has taught many college biology courses.

Learn how a nuclear membrane functions, and learn the parts of a nuclear membrane. Find the differences between animal cell and plant cell nuclear membranes. Updated: 03/30/2021

Nuclear Membrane Definition

What is a nuclear membrane? The nuclear membrane, also known as the nuclear envelope, is the outer covering of the nucleus. The nuclear membrane separates the nucleus from the cytoplasm and helps to protect its contents, the DNA of the cell. Only eukaryotic cells have a nucleus. Animals, plants and fungi are examples of eukaryotic cells. But, do prokaryotes have a nuclear membrane? The answer is no. Prokaryotic cells do not have a nucleus and thus do not have a nuclear membrane. Only eukaryotic cells have a nuclear membrane.

Nucleus diagram

diagram showing the parts of the nucleus including the nuclear membrane

Animal Cell Nuclear Membrane

Animal cells are eukaryotic and thus have a nucleus and a nuclear membrane. The function of the animal cell nuclear membrane is to protect the contents of the nucleus and to separate it from the cytoplasm. The animal cell nuclear membrane contains animal specific proteins on the surface of the membrane, which distinguish it from fungal or plant nuclear membranes. Animal cells also have special organelles called centrosomes that help position the nucleus and assist in cell division.

Centrosomes are microtubule structures unique to animal cells and exist within the cytoplasm. Centrosomes are important to animal cell division, called mitosis.

Animal cell nuclear membrane

animal cell nuclear membrane diagram

During mitosis, there are multiple phases. One of the first questions students often ask is, when does the nuclear membrane dissolve? The nuclear membrane must dissolve early on in mitosis in order to release the DNA prepare the DNA for cell division. Thus, the nuclear membrane usually dissolves in prophase, the first phase of mitosis. Centrosomes attach to the DNA and help position them to move to opposite sides of the cell. So, after this, in which phase does a new nuclear membrane develop? A new nuclear membrane reforms during telophase, the last phase of mitosis.

Plant Cell Nuclear Membrane

Plant cells are also eukaryotic cells and thus have a nucleus and a nuclear membrane. Despite having the same overall structure, plant cell nuclei and nuclear membranes are slightly different than those in animal cells. Plant cells lack centrosomes altogether and rely solely on the nuclear membrane in mitosis to organize the chromosomes. Plant cell nuclear membranes also contain different proteins than animal cells.

Definition of Nuclear Membrane

All eukaryotic cells (those found in animals, plants, protists, and fungi) have a control center called the nucleus. This is where genetic material, or DNA, is stored. Surrounding every nucleus is a double-layered membrane called the nuclear membrane or nuclear envelope. This membrane separates the nucleoplasm, or fluid inside the nucleus, from the cytoplasm, or the fluid outside the nucleus.

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  • 0:01 Definition of Nuclear Membrane
  • 0:30 Appearance of Nuclear Membrane
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Plant cell nuclear membrane

plant cell nuclear membrane diagram

Nuclear Membrane Function

The next question to address is what does the nuclear membrane do? The main nuclear membrane function is to separate the nucleus from the rest of the cell and to protect the DNA. However, the nuclear membrane also plays other important roles in the cell, including the following:

  • Separates the nucleus from the rest of the cell and prevent unwanted materials from entering the nucleus
  • Regulates what enters and leaves the nucleus through nuclear pores and nuclear localization signals
  • Regulates gene transcription through the movement of transcription factors

Nuclear Membrane Structure

A nuclear membrane definition includes both its function and structure. The nuclear membrane's function is to protect the contents of the nucleus, but its structure is what allows it to do so. The following are important parts of the nuclear membrane description:

  • Outer nuclear membrane
  • Inner nuclear membrane
  • Nucleolus
  • Nucleoplasm
  • Nuclear pores

Nuclear membrane structure

A detailed diagram of the nuclear membrane structure

Outer Nuclear Membrane

The outer nuclear membrane is the outermost barrier of the nucleus. The outer nuclear membrane is continuous with the membrane of the rough endoplasmic reticulum (rough ER). This membrane is studded with ribosomes that participate in protein synthesis.

Inner Nuclear Membrane

The inner nuclear membrane is the inner barrier of the nucleus. The space between the inner and outer nuclear membranes is called the perinuclear space. The inner part of the inner nuclear membrane is connected to the nuclear lamina, a mesh-like network of proteins. The inner lamina contains proteins that help anchor the DNA and chromatin into place. The nuclear lamina is also important because it helps direct materials for export through the nuclear pores. It also is thought to play a role in dissolving the nuclear membrane during mitosis.

Appearance of Nuclear Membrane

A nuclear envelope is made up of two membranes: an outer membrane and an inner membrane. Each membrane is composed of phospholipids arranged in a bilayer. This means that the entire nuclear membrane has four rows of phospholipids. The inner and outer membranes are separated by the perinuclear space.

The outer nuclear membrane is continuous with the rough endoplasmic reticulum, an organelle important in making and transporting proteins. Both the rough endoplasmic reticulum and the outer nuclear membrane are covered in ribosomes, which are the actual sites of protein synthesis.

Attached to the inner nuclear membrane on the nucleoplasm side is the nuclear lamina. This is a sheet of proteins that provides support for and strengthens the nuclear envelope. The nuclear lamina also attaches to and anchors chromatin, loosely arranged DNA and protein.

Function of Nuclear Membrane

The nuclear membrane keeps your DNA inside the nucleus to protect it from surrounding substances in the cytoplasm. Additionally, the nuclear envelope can regulate what materials enter or exit the nucleus. Anything that needs to pass between the nucleoplasm and the cytoplasm can only do so through holes in the membrane called nuclear pores.

Nuclear pores only allow very small molecules, ions, or proteins to freely move into or out of the nucleus. Any large molecules that need to cross the nuclear membrane must have the appropriate labels. Proteins lining the nuclear pores will recognize these labels or tags and let the molecules cross. There are two kinds of tags: the nuclear localization signal and the nuclear export signal.

A nuclear localization signal (NLS) is a short amino acid sequence that tags a molecule for entry into the nucleus. Large molecules that are needed for DNA replication or transcription in the nucleus must have the NLS. This will allow them to be recognized and escorted into the nucleoplasm by nuclear pore proteins.

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Video Transcript

Definition of Nuclear Membrane

All eukaryotic cells (those found in animals, plants, protists, and fungi) have a control center called the nucleus. This is where genetic material, or DNA, is stored. Surrounding every nucleus is a double-layered membrane called the nuclear membrane or nuclear envelope. This membrane separates the nucleoplasm, or fluid inside the nucleus, from the cytoplasm, or the fluid outside the nucleus.

Appearance of Nuclear Membrane

A nuclear envelope is made up of two membranes: an outer membrane and an inner membrane. Each membrane is composed of phospholipids arranged in a bilayer. This means that the entire nuclear membrane has four rows of phospholipids. The inner and outer membranes are separated by the perinuclear space.

The outer nuclear membrane is continuous with the rough endoplasmic reticulum, an organelle important in making and transporting proteins. Both the rough endoplasmic reticulum and the outer nuclear membrane are covered in ribosomes, which are the actual sites of protein synthesis.

Attached to the inner nuclear membrane on the nucleoplasm side is the nuclear lamina. This is a sheet of proteins that provides support for and strengthens the nuclear envelope. The nuclear lamina also attaches to and anchors chromatin, loosely arranged DNA and protein.

Function of Nuclear Membrane

The nuclear membrane keeps your DNA inside the nucleus to protect it from surrounding substances in the cytoplasm. Additionally, the nuclear envelope can regulate what materials enter or exit the nucleus. Anything that needs to pass between the nucleoplasm and the cytoplasm can only do so through holes in the membrane called nuclear pores.

Nuclear pores only allow very small molecules, ions, or proteins to freely move into or out of the nucleus. Any large molecules that need to cross the nuclear membrane must have the appropriate labels. Proteins lining the nuclear pores will recognize these labels or tags and let the molecules cross. There are two kinds of tags: the nuclear localization signal and the nuclear export signal.

A nuclear localization signal (NLS) is a short amino acid sequence that tags a molecule for entry into the nucleus. Large molecules that are needed for DNA replication or transcription in the nucleus must have the NLS. This will allow them to be recognized and escorted into the nucleoplasm by nuclear pore proteins.

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