Final answer:
Post-translational modifications of histone proteins, such as histone acetylation, methylation, and phosphorylation, alter the charge and interaction of histones with DNA, affecting chromatin structure and gene expression.
Step-by-step explanation:
Post-translational modifications (PTMs) are chemical changes that occur on histone proteins after they have been synthesized. These modifications can include histone acetylation, histone methylation, and histone phosphorylation. PTMs can significantly alter the electrostatic interactions between the histones and DNA, which thereby influences how tightly DNA is wrapped around the histones, affecting the accessibility of DNA for transcription and ultimately gene expression.
During histone acetylation, acetyl groups are attached to lysine residues in the histone tails, which reduces the positive charge on the histones, thereby loosening the interaction with the negatively charged DNA. Consequently, the chromatin becomes more relaxed, making the DNA more accessible for transcription. Histone kinases add phosphate groups to histones, resulting in histone phosphorylation, which again alters the interaction with DNA by changing the charge of histones. Histone methyl transferases catalyze the transfer of methyl groups to lysine and arginine residues on histones, known as histone methylation, which can either repress or activate gene expression depending on the specific sites and number of methylations.