Which one of the following statements about Histones is wrong ?

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

1. Charge and Composition:
DNA is a negatively charged molecule due to the phosphate groups in its backbone. To package DNA efficiently inside the cell nucleus, it wraps around histones. Therefore, histones must carry a positive charge to attract and bind the negatively charged DNA. The positive charge of histones is due to the abundance of basic amino acids, specifically Lysine and Arginine, which have positively charged side chains at physiological pH. Thus, the statements "Histones carry positive charge in the side chain" and "Histones are rich in amino acids - Lysine and Arginine" are correct.

2. Structural Organization:
Histones organize to form a structure called the nucleosome core particle. This core is an octamer, meaning it is a unit composed of 8 molecules (two copies each of histones H2A, H2B, H3, and H4). Thus, the statement "Histones are organized to form a unit of 8 molecules" is correct.

3. pH and Basic Nature:
Because histones are rich in basic amino acids (Lysine and Arginine), they are basic in nature, not acidic. Consequently, their pH is basic (alkaline), which allows them to maintain a positive charge under physiological conditions. Therefore, the statement "The pH of histones is slightly acidic" is false.

Conclusion:
The wrong statement is that the pH of histones is slightly acidic.