Which one of the following statements about Histones is wrong?

Histones are proteins that bind DNA in the nucleus to form nucleosomes, the fundamental units of chromatin.

Key properties of histones relevant to evaluating the statements:

1. Amino‑acid composition: Histones contain a high proportion of positively charged basic residues, especially lysine (K) and arginine (R). These residues facilitate strong electrostatic interactions with the negatively charged phosphate backbone of DNA.

2. Charge of side chains: Because lysine and arginine have side‑chain pKa values around 10.5 and 12.5 respectively, they remain protonated (positively charged) at physiological pH (~7.4). Consequently, histones carry an overall positive charge.

3. Quaternary organization: In eukaryotic cells, eight histone proteins (two each of H2A, H2B, H3, and H4) assemble into an octameric core around which ~146 base pairs of DNA wrap, forming a nucleosome.

4. Isoelectric point (pI) and pH: The abundance of basic residues gives histones a high isoelectric point, typically pI ≈ 10–11. At a pH lower than the pI, a protein carries a net positive charge; at a pH higher than the pI, it becomes negatively charged. Since the cellular environment (pH ≈ 7.4) is well below the histone pI, histones are positively charged and the surrounding pH is considered neutral to slightly basic, not acidic.

Evaluating each option:

• “Histones are rich in amino acids – Lysine and Arginine” – true, as explained in point 1.

• “Histones carry positive charge in the side chain” – true, due to protonated lysine/arginine side chains (point 2).

• “Histones are organized to form a unit of 8 molecules” – true, describing the histone octamer (point 3).

• “The pH of histones is slightly acidic” – incorrect. Histones have a high pI and are basic; they function in a neutral‑to‑basic environment, not an acidic one.

Therefore, the statement that “The pH of histones is slightly acidic” is the wrong statement.