Which of the following statements are correct regarding nucleosome and packaging of DNA helix?
A. A typical nucleosome contains 200 bp of DNA helix.
B. The positively charged DNA is wrapped around the negatively charged histone octamer to form a structure called nucleosome.
C. Nucleosomes in chromatin are seen as ‘beads-on-string’ structure when viewed under electron microscope.
D. Chromatin packaging at higher level requires non-histone chromosomal proteins.
Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → A, C and D only
The DNA of a eukaryote is packed with proteins called histones. Histones are rich in the basic amino acids lysine and arginine, so they carry a positive charge. DNA carries a negative charge. This is why the two bind.
A. A typical nucleosome contains 200 bp of DNA helix. — Correct. A nucleosome is the repeating unit of chromatin, with about 200 bp of DNA.
B. The positively charged DNA is wrapped around the negatively charged histone octamer to form a structure called nucleosome. — Incorrect. The charges are reversed for the two. DNA is negatively charged and the histone octamer is positively charged.
C. Nucleosomes in chromatin are seen as ‘beads-on-string’ structure when viewed under electron microscope. — Correct. Each bead is a nucleosome, and the string is the DNA between the beads.
D. Chromatin packaging at higher level requires non-histone chromosomal proteins. — Correct. The beads-on-string fibre is coiled and condensed further with the help of non-histone chromosomal (NHC) proteins.
NCERT Extract:
Packaging of DNA Helix – …
