Final answer:
Histones consist of high levels of the basic amino acids lysine and arginine, which have positively charged side chains essential for binding DNA and forming nucleosomes.
Step-by-step explanation:
Histones are basic proteins that play a crucial role in the packaging of DNA in the nucleus of eukaryotic cells. They contain an unusually high amount of the basic amino acids lysine and arginine. These amino acids have positively charged side chains, which are conducive to binding with the negatively charged phosphodiester backbone of DNA. This interaction is vital for the formation of nucleosomes, where DNA wraps around an octamer of histones, comprising two each of the four histone proteins. The side chains of lysine and arginine contribute significantly to the histone's ability to engage in these interactions due to their positive charge at physiological pH. Histidine is also considered a basic amino acid but is less often ionized at physiological pH, although it can gain a positive charge in more acidic environments, below a pH of 6.0.