What is caryoplasm?

The karyoplasm is also called nuclear plasma or nucleoplasm. It describes the structures that lie within the nuclear membrane. In contrast, there is also the cytoplasm, which is bounded by the outer cell membrane (plasma membrane).

These two spaces consist largely of water and various additives. An important difference between karyoplasm and cytoplasm are the different concentrations of electrolytes, such as Cl- (chloride) and Na+(sodium). This special milieu in the karyoplasm provides the optimal environment for the processes of replication and transcription. The karyoplasm also contains the chromatin, which contains the genetic material, and the nucleolus.

Nucleus size

Eukaryotic cell nuclei usually have a roundish shape and a diameter of 5 – 16 μm. The conspicuous nucleolus is clearly visible under the light microscope and has a diameter of 2 – 6 μm. In general, the appearance and size of the nucleus is strongly dependent on cell type and species.

The double membrane of the cell nucleus

The cell nucleus is separated from the cytoplasm by a double membrane. This double membrane is called the nuclear envelope and consists of an inner and an outer nuclear membrane, with the perinuclear space in between. Both membranes are connected by pores and thus form a physiological unit (see next section).

In general, double membranes always consist of a lipid bilayer in which different proteins are embedded. These proteins can be modified with different sugar residues and enable the specific biological functions of the nuclear membrane. Like all double membranes, the nuclear envelope has both a water-loving (hydrophilic) and a water-avoiding (hydrophobic) part and is therefore fat- and water-soluble (amphiphilic).In aqueous solutions, the polar lipids of the bilayer form aggregates and arrange themselves in such a way that the hydrophilic part is facing the water, whereas the hydrophobic parts of the bilayer are adjacent to each other. This special structure creates the conditions for the selective permeability of the double membrane, i.e. cell membranes are only permeable for certain substances. In addition to the regulated exchange of substances, the nuclear envelope also serves to delimit (compartmentalize) the cell nucleus and forms a physiological barrier so that only certain substances can enter and leave the cell nucleus.