Paper protein paper in genetic transcription
Histones are characterized by being small proteins that belong to chromatin with specific functions, such as H1. This histone is characterized by being connector and responsible for unwinding the fiber of 30 Nm, either in Zigzag or in solenoid (Karp, 2014). The H1 Histonian H1 joins the DNA that enters and leaves the nucleosomic nucleus particle and has an important role in the establishment and maintenance of chromatin structures of higher order. Each H1 is made up of certain proteins related to different species. However, in eukaryotes they have the same structure (Izzo, Kamieniarz and Schneider, 2008).
It is believed that there are several hierarchical levels of DNA packing in chromatin, from a 10 Nm chromatin fiber (lower level of chromatin) that is packaged in a 30 nm fiber. It is believed that the transitions between the fibers of 30 Nm and 10 Nm are essential for the control of the transcriptional state of the chromatin (Razin and Gavrilov, 2014). The most accepted model of the fiber of the 30 Nm is that of Zigzag, where nucleosomes are being interactive neighbors and are successively found in the DNA. Its assembly increases the packing rate between 6 and 40 times and is maintained according to how histones and nucleosomes are. With the help of histone H1, it unwinds in Zigzag or solenoid, which is characterized by a curvature of the helical structure of 6 to 8 nucleosomes in each lap (Karp, 2014). They belong to the third level of DNA packaging, where chromatin is organized in the form of 30 nm fiber handle and remain in that structure thanks to cohesine rings. They are characterized by being super -colored reaching a compaction level of 80 to 100 nm. One of the characteristics is that their bases are united with residual proteins from scaffolding. They are only visible when mitotic chromosomes are isolated and their compaction level increases in mitosis (Karp, 2014).
Cohesine are annular proteins that keep DNA in these loops. They are of great importance since the replicated DNA is kept when the mitosis is being performed (Karp, 2014). Cohesine is also necessary for damaged DNA repair and has important functions in the regulation of gene expression in both proliferative and post -mitotic cells. In vertebrates, cohesine complexes are also associated with WAPP.
Optional heterochromatin is a chromatin less dense than constitutive heterochromatin, it is not repetitive and is inactive in some differentiated cells or in certain phases of life. This chromatin can lose its condensate status and become transcriptionally active. His condensed state, therefore, is not permanent. One of the characteristics of this heterochromatin is the presence of repeated line -type sequences. These sequences, scattered throughout the genome, could promote the spread of a condensed chromatin structure. An example of this heterochromatin is in mammalian cells, where one of the female X chromosomes has transcriptional activity and the other X chromosome is inactive, known as Barr’s corpusculus (Karp, 2014; Mattei and Luciani, 2003).
Constitutive heterochromatin is DNA that is not permanently transcribed, and always remains in a compact state. In the mammalian cells, this chromatin is located between the centromeres, telomers of each flanking region and in the arm of the chromosomes and. Unlike optional heterochromatin, if it has repetitive sequences, few genes, it is stable and retains its heterochromatic properties during all stages of development and in all tissues. These genes that are active, when moving in this region, come to inactivate. Another characteristic of this heterochromatin is the inhibition of genetic recombination, which can produce DNA deletion or duplication (Karp, 2014; Mattei and Luciani, 2003).
It is a hypothesis that suggests that the transcription of genetic information encoded in the DNA is partly regulated by chemical modifications of histone proteins, mainly at their unstructured ends (Xing and Hall, 2013; Karp, 2014). In addition, it expresses how the status of chromatin activity is located and how the histone code influences its structure and function. The first postulate suggests that modified waste act as specific protein assembly places, which determine chromatin activity. The second postulate suggests that these waste alters the interaction of histone tails with DNA or with each other (Karp, 2014).
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