Nuclear envelope

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Nuclear membrane, schematic drawing

The nuclear envelope or nuclear membrane is the double membrane of the nucleus of a eukaryotic cell . The membrane resembles the cell membrane in its structure, consisting of a double layer of phospholipids, and encloses the perinuclear space. The outer membrane is occupied by ribosomes and merges into the endoplasmic reticulum (ER) in some places , so that this perinuclear gap connects the nuclear lumen and the ER. A 30–100 nm thick layer of intermediate lamin filaments (nuclear lamina) borders the inner membrane towards the core . They stabilize the cell nucleus, serve as a fixation for the chromatin threads and are broken down and rebuilt during mitosis .

Core pore, schematic drawing

There are numerous nuclear pores in the nuclear envelope that ensure the controlled exchange of large molecules between the nuclear and cell plasma. At these points the outer and inner nuclear membrane connect and the pore is surrounded by a ring of 8 subunits, which protrude into the pore with a spoke-like extension. In the center there is a “plug” that controls the transport of the material. The pore has a diameter of 10 nm and can expand up to 26 nm. Molecules with a molar mass of more than 60,000 Daltons cannot pass through the pore. This prevents ribosomes from getting into the nucleus.

During a nuclear division, which is part of a cell division , the nuclear envelope is dissolved in order to be able to distribute the chromosomes better. After the division has taken place, the nuclear envelope is re-formed around the cell nuclei of the two daughter cells. Lamines are involved in the breakdown and regeneration of the membrane.

literature

  • Jeremy M. Berg, John L. Tymoczko, Lubert Stryer : Biochemistry. 6 edition, Spektrum Akademischer Verlag, Heidelberg 2007. ISBN 978-3-8274-1800-5 .
  • Donald Voet, Judith G. Voet: Biochemistry. 3rd edition, John Wiley & Sons, New York 2004. ISBN 0-471-19350-X .
  • Bruce Alberts , Alexander Johnson, Peter Walter, Julian Lewis, Martin Raff, Keith Roberts: Molecular Biology of the Cell , 5th Edition, Taylor & Francis 2007, ISBN 978-0815341062 .