What are histones?
histones are structures in eukaryotic cells and some unicellular microorganisms of phylum euryarchaeot, which serve as coils around which deoxyribonucleic acid (DNA) is very carefully packed. Without maintaining the space that the histones allow, cells could not contain their own DNA. Histons also play an important role in the expression of the gene by allowing or preventing the approach of transcription molecules to DNA genes. The third task is to maintain structural integrity of DNA and much larger chromosome. The most common proteins are called H1/H5, H2A, H2B, H3 and H4. DNA is tied to histones of attractions between side groups of histone proteins and DNA. This attractive force is modified by adding acetyl or methyl groups to several amino acids of lysine or arginine at the end of the H3 and H4 proteins. The tightening or loosening of the DNA source results in available or inaccessible genes known as the turn of the "ON" or "OFF" gene.
In most cells, regardless of the source, they form eight histone proteins, consisting of two of H2A, H2B, H3 and H4, form an octare structure. Approximately 146 pairs of DNA packaging wrapped around the octare structure almost twice to form a "nucleosom". A short DNA loop, stabilized by H1 or its H5 analogue, leads to another nucleosome and creates a structure that is often characterized as "beads on the chain". Nucleosomes and their interconnected DNA cuts form tight spirals with six nucleosomes on the curve to make the so -called chromatin fibers. The fibers pack together to form a chromosome.
Histon proteins H2A, H2B, H3 and H4 have a relatively low molecular weight consisting of 120 to 135 amino acids per protein molecule. H1/H5 histones are much longer and give a gradual frame on nucleosomes, similar to a steel rod connecting a number of discs. In human cells, if all DNAs were unravel and laid to the end, the spring would be about 70 inches long (1.8 m),But only about 0.0000007 inch (180 nanometers). By hitting and retrospectively, the propagation of substructures works, there are 23 pairs of chromosomes in the core, which is less than 0.0004 inches (10 micrometers) on average. Histons do this folding possible control of the molecular environment.
It was assumed that the histones were initially only the above types. However, the research pointed to a much greater diversity than it was previously accepted. The basic molecules are still relatively the same among organisms that differ as yeast and mammals. This feature is called evolutionary protection. This means that even small changes in these molecules lead to cells that either could not prosper or reproduce and cause damage and evolutionary punishment of organicism.