Synaptonemal complex
The synaptonemal complex (or synaptic complex) is about 100-300 nm wide structure of proteins, RNA and DNA, which can be observed in certain phases of the meiosis in the nucleus. It provides the pairing of homologous chromosomes and enables controlled mixing of paternal and maternal genetic information in the process of crossing over.
The synaptonemal complex is a bonding site in the nucleus. During meiosis, this complex is formed by the arrangement of the homologous chromatid threads easier.
This complex appears scalariform. The " rungs of the ladder " and the location in the middle structure is called the central element. It is connected on both sides with the lateral element (page element). Store in this page elements to one side, the paternal sister chromatids and the other maternal sister to.
This results in the following order: paternal sister chromatids 1 2 - Lateral Element - Central Element - Lateral Element - maternal sister chromatids 3 4
In the central element can be found at greater distances from each other Umkopplungsknoten. Here, the recombination ( chiasm, recoupling ) takes place. This genetic information of maternal chromatids are exchanged through the central element area away against homologous sections of paternal genetic information to the other side (and vice versa).
The synaptonemal complex forms in zygotene. After pachytene it dissolves, because the chromosome pairing is now complete. If the complex does not dissolve, it would be no recombination or division.
Development and function
The precursor structures of the synaptonemal complex formed already at the stage of Leptotäns meiosis. The sister chromatids of the chromosomes condense and then self-assemble into a so-called Lateralelement, a structure reminiscent of the left or right half of a zipper in the electron microscope. Each "tooth" of the zipper half is called Synaptomer, and consists of highly compacted chromatin and additional proteins.
During the homolog pairing ( synapsis ) each supporting a Lateralelement with its homologous partner together (ie the paternal with maternal chromosome). The Synapsis starts at the ends of Lateralelemente which continues to agglomerate together, equal a closing zipper. Here, the information on the merging overlapping DNA strands plays a controlling role, since that usually involve only find sections with "comparable " information.
Are the Lateralelemente together ( the zipper closed at one point ), so forms between the Lateralelementen a protein band ( the central element ). With the formation of the central element of the synaptonemal complex is completed. The entire structure now holds together the homologous DNA regions of the paternal and maternal genetic information in space for a certain amount of time, allowing the exchange of homologous paternal and maternal gene segments.