Which of the following statements are correct with reference to packaging of DNA helix ?

A. Histones are organized to form a unit of eight molecules called histone octamer.
B. Histones are negatively charged, basic proteins.
C. Histones are rich in the basic amino acid residues– lysine and arginine.
D. The positively charged DNA is wrapped around the histone octamer to form nucleosome.
E. The packaging of chromatin at higher levels requires an additional set of proteins called non-histone chromosomal proteins.

Choose the correct answer from the options given below :

To decide which statements are correct, evaluate each one against known facts about DNA packaging.

Statement A: “Histones are organized to form a unit of eight molecules called histone octamer.”
- Histone proteins H2A, H2B, H3, and H4 each exist as a pair (two copies).
- These four dimers combine to make a histone octamer (8 molecules).
- This octamer is the core around which DNA is wrapped.
=> Statement A is true.

Statement B: “Histones are negatively charged, basic proteins.”
- Histones contain many lysine and arginine residues, giving them a net positive charge at physiological pH.
- Therefore they are **positively**, not negatively, charged.
=> Statement B is false.

Statement C: “Histones are rich in the basic amino‑acid residues– lysine and arginine.”
- The high proportion of lysine and arginine residues is why histones are basic and bind DNA.
=> Statement C is true.

Statement D: “The positively charged DNA is wrapped around the histone octamer to form nucleosome.”
- DNA has a phosphate backbone that carries a **negative** charge.
- The nucleosome is formed by negatively charged DNA wrapping around the positively charged histone octamer.
=> The phrase “positively charged DNA” is incorrect, so **Statement D is false**.

Statement E: “The packaging of chromatin at higher levels requires an additional set of proteins called non‑histone chromosomal proteins.”
- Beyond the nucleosome, chromatin fibers are further organized by linker histones (e.g., H1) and a variety of non‑histone chromosomal proteins (e.g., scaffold‑associated factors).
=> Statement E is true.

Summarizing the truth values:

• A – true
• B – false
• C – true
• D – false
• E – true

Therefore the correct combination of statements is **A, C and E only**.