The karyoplasm is the name given to the protoplasm within cell nuclei, which differs from the cytoplasm particularly in its electrolyte concentration. For DNA replication and transcription, the karyoplasm provides an optimal environment. In diabetic patients, nuclear inclusions of glycogen may be present in the karyoplasm.
What is karyoplasm?
Cell nuclei are located in the cytoplasm. They are round-shaped organelles of eukaryotic cells. The nucleus contains the genetic material of a cell. All nuclei are separated from the cytoplasm by a double membrane. This double matrix is called the nuclear envelope. In it, the genetic material is present as deoxyribonucleic acid. The terms nuclear and karyo make reference to the cell nuclei. The Greek term karyon means nucleus. The karyoplasm is thus the nuclear plasma or nucleoplasm of cell nuclei. This is the entire contents of the cell nucleus behind the nuclear envelope. The main components of the nucleus content are chromatin, filamentous decondensed chromosomes and nucleoli. Thus, the karyoplasm is a part of the protoplasm. This is understood to be the cell fluid including its colloidal components. The protoplasm is formed by the karyoplasm and the cytoplasm. The living part of the cell is the cytoplasm enclosed externally by cell membrane. The nuclear membrane separates the two forms of plasma. The karyoplasm differs from the cytoplasm mainly in the concentration of dissolved electrolytes. The karyolymph corresponds to unstructured karyoplasm. It is called nuclear juice and is interspersed with the protein scaffold of the nuclear matrix. The karyoplasm interacts with the cytoplasm via nuclear pores.
Anatomy and structure
The karyoplasm mainly contains water. Light microscopically, it appears homogeneous in an unstained preparation. In places, darker condensations may appear. These condensations are the nuclear bodies or nucleoli and the granules of chromatin. Chromatin is a clumping and precipitation of fine chromosomal fibrils. In them, after staining, the chromocenters can be seen as larger chunks. The chromatin density in the karyoplasm depends on the cell activity. Chromatin always contains nucleoproteins, DNA, histone proteins and non-histone proteins. The junctions of chromosome arms are called centromeres. Lighter chromatin regions correspond to loose chromatin. Darker regions correspond to the more electron dense chromatin regions where chromatin tends to clump. The lighter euchromatin of the karyoplasm can be distinguished from the more electron dense and darker heterochromatin. There is smooth transition between the two areas. Longer portions of unused DNA lie clustered together in heterochromatin clumps of histone proteins. In contrast, functionally relevant DNA segments lie in euchromatin.
Function and tasks
From the nucleus, every cell is controlled. Just about all of the cells’ genetic information is located in the karyoplasm of the cell nuclei. The genetic material of the karyoplasm only comes into view during cell division and is otherwise in unstructured form. All metabolic processes of a cell take place in the karyoplasm via RNA messenger molecules. The karyoplasm also provides an ideal environment for the processes of transcription and replication. Transcription involves the transfer of genetic information from the cell nuclei to RNA. This process takes place on one of the two strands. The DNA strand takes on the role of a matrix. Its base sequences are complementary to the RNA. Transcription takes place in the cell nucleus with the help of the catalysis of DNA-dependent RNA polymerases. In eukaryotic cells, this forms an intermediate known as hnRNA. Post-transcriptional modification turns this intermediate into mRNA. For these processes, the nuclear plasma establishes the necessary environmental conditions. The same is true for the processes of replication, in which a copy of DNA is made. Last but not least, the karyoplasm has mitotic significance. In its so-called working nucleus, the mitotic interphase contains the user hereditary information in its non-condensed and bundled form as well as in the euchromatin network. Once mitosis has begun in the nucleus, condensations of chromatin take place in the karyoplasm of the cell. Thus, chromatin is again present in a multiply spiraled and highly ordered form, yielding chromosomes.
Diseases
Cellular damage is often examined histologically.This examination allows the nature of the damage to be determined in more detail. Cell damage due to nuclear inclusions in the affected cell nuclei can often be observed in this context. The inclusions may consist of components of the cytoplasm or foreign substances. Cytoplasmic nuclear inclusions are the most common form. They may result from invagination of the nuclear envelope, as seen in tumors. Sometimes, however, cytoplasmic structures are included in the newly forming daughter nuclei during telophase. This phenomenon may be present, for example, in colchicine poisoning. Usually, such inclusions are separated from the karyoplasm by nuclear envelope portions and show degeneration. However, they can also penetrate into the karyoplasm. This is often the case with glycogen inclusions, as seen in diabetics. Smaller particles of glycogen probably penetrate from the cytoplasm through nuclear pores into the karyoplasm, where they form large aggregates. However, it is also possible that the karyoplasm synthesizes the glycogen and allows it to polymerize into larger particles. In addition to infections, nuclear inclusions are associated primarily with poisoning. The inclusions can have severe effects on mitosis. For example, if the interphase nucleus undergoes a manifest change, negative consequences for the cells and the entire organism set in. These connections are mainly discussed in the context of growth disorders. The karyoplasm can also completely escape from a cell nucleus in the context of ruptures of the membrane. This connection is exploited by the icing method of dermatology.
