Core matrix
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| Cell nucleus |
| Gene Ontology |
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| QuickGO |
Multicellular organisms are characterized by differentiated , that is, specialized cells , which in turn have a characteristic architecture and ways of communicating with one another. Both components - structure and interaction - are mediated by protein networks that are connected to one another via contact points. From the outside ( extracellular space ) to the inside ( cell nucleus ) these networks are:
- the extracellular matrix , mostly specialized collagen braids that are produced and secreted by the embedded cell itself,
- the cytoskeleton made of microtubules , actin or microfilaments and intermediate filaments ,
- as well as the nuclear skeleton, also called the nuclear matrix . Outstanding components here are the lamines , which are located in the nuclear envelope and, as we now know, also inside the cell nucleus, and SAF-A ( scaffold-attachment factor A , also described as hnRNP-U). It also contains cell-specific factors that have recently become important in the diagnosis of malignant degeneration.
This means that nucleated cells of higher living beings ( eukaryotes ) have a much more complicated structure than bacterial cells . The fundamental difference is the nuclear membrane , which separates the caryoplasm with nuclear DNA from the cytoplasm . Each of the 46 chromosomes of a human cell contains between 48 and 240 million base pairs , which corresponds to a length of 1.6 to 8.2 cm (a total of 2 m contour length of DNA). How can a thread of this length disappear in a core with a diameter of 5–30 µm (micrometers)? The secret lies in the ordering principles of chromatin , a complex of DNA , RNA and proteins , which together enable a regular folding in several stages and thus a diverse epigenetic regulation of gene expression . The lower levels contain the nucleosome , discovered in 1974 , a complex of DNA and proteins ( histones ) around which the DNA is wrapped in about two turns. The total of 25 million nucleosomes of a mammalian cell are in turn organized in the form of 30,000 loop-shaped chromatin domains (figure). According to a classic model, this loop organization is maintained by the attachment of certain DNA elements called S / MARs ( scaffold / matrix attachment regions) to the protein backbone of the cell nucleus (the nuclear matrix ; gray fields).
More recent studies indicate that this complex structure has a considerable dynamic, which is also determined by the type and state of differentiation of the cell.
See also
literature
- HHQ Heng, S. Goetze, CJ Ye, W. Lu, G. Liu, S. Bremer, M. Hughes, J. Bode, SA Krawetz: Dynamic features of scaffold / matrix attached regions (S / MARs) in anchoring chromatin loops . In: J. Cell Sci. 117, 2004, pp. 999-1008.