Charge neutralization Chromosomes

Fig.l The dynamic equilibrium between acetylation and deacetylation of lysine residues of the histones is controlled by the opposing enzymatic activities of HATs and HDACs. The acetylation status determines whether a lysine residue is either neutral (acetylated) or positively charged (deacetylated). The consequent changes in the internucleosomal interactions and condensation status of chromosomal domains govern the transcriptional competence of DNA ( Diane Bruyninckx)... 

Proteins help to compact DNA this is important because the DNA in a chromosome could not fit inside its cell if it were not compacted. Histones are positively charged proteins that neutralize negative DNA strands when they wrap around and form complexes with the DNA. This wrapped structure, called beads on a string, represents the first level of compaction. The beads are condensed to form fibers, fibers fold into loops, loops combine with nuclear scaffold proteins to form rosettes, and rosettes condense to form coils. Finally, a chromatid with ten or more coils is formed. Nonhistone proteins within chromosomes are also important. These proteins have varied functions, including assisting in the unwinding of DNA and in the repairing of DNA. 

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