Which one of the following statements about Histones is wrong?

To determine which statement about histones is incorrect, let us analyze the structural and chemical properties of histones step-by-step:

1. What are Histones?
Histones are highly alkaline proteins found in eukaryotic cell nuclei. Their primary function is to package and order the DNA into structural units called nucleosomes. DNA is negatively charged due to the phosphate groups in its backbone, so histones must have properties that allow them to bind tightly to DNA.

2. Charge and Amino Acid Composition:
Histones carry a net positive charge. This positive charge is due to an abundance of basic amino acid residues, specifically Lysine and Arginine. The side chains of these amino acids contain amino groups that are protonated and positively charged at physiological pH, allowing them to interact electrostatically with the negatively charged DNA. Therefore, the statements "Histones carry positive charge in the side chain" and "Histones are rich in amino acids - Lysine and Arginine" are biologically correct.

3. Structural Organization:
Histones organize to form an octamer, which is a unit composed of 8 histone molecules (two molecules each of H2A, H2B, H3, and H4). DNA winds around this octamer core to form a nucleosome. Thus, the statement "Histones are organized to form a unit of 8 molecules" is also correct.

4. pH of Histones:
Because histones are rich in basic amino acids (Lysine and Arginine), they are basic proteins. Basic substances have a pH value greater than 7, not acidic (which would be less than 7). Consequently, the pH of histones is basic (alkaline), making the statement "The pH of histones is slightly acidic" incorrect.

Thus, the wrong statement about histones is "The pH of histones is slightly acidic".