Figure showing packaging of DNA Helix. Observe the figure and answer the following questions.
Which part of the nucleosome is positively charged?
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → Histone octamer
Option (1) Histone octamer — Correct. Histones are rich in the basic amino acids lysine and arginine, so they carry a positive charge. The histone octamer is therefore the positively charged part, and the negatively charged DNA wraps around it.
Option (2) Chromatin — Incorrect. Chromatin is made of DNA and histones together, so it includes the negatively charged DNA. It is not the positively charged part of the nucleosome.
Option (3) DNA — Incorrect. DNA is negatively charged because of its phosphate groups. It is wrapped around the positively charged histone octamer.
Option (4) Heterochromatin — Incorrect. Heterochromatin is densely packed chromatin, not a charged part of the nucleosome.
NCERT Extract:
Packaging of DNA Helix – “… In eukaryotes, this organisation is much more complex. There is a set of positively charged, basic proteins called histones. A protein acquires charge depending upon the abundance of amino acids residues with charged side chains. Histones are rich in the basic amino acid residues lysine and arginine. Both the amino acid residues carry positive charges in their side chains.”
Packaging of DNA Helix – “… The negatively charged DNA is wrapped around the positively charged histone octamer to form a structure called nucleosome (Figure 5.4 a).”