Read the given passage and answer the questions that follow:
In prokaryotes such as E. coli, though they do not have a defined nucleus the DNA is not scattered throughout the cell. The DNA is held with some proteins in a specific region. In eukaryotes this organisation is much more complex. There is a set of positively charged basic proteins called histones. Histones are organised to form a unit of 8 molecules called histone octamer. The negatively charged DNA is wrapped around the positively charged histone octamer.
How many base pairs does a typical nucleosome of DNA helix contain?
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → 200
A nucleosome is the unit formed when DNA wraps around a histone octamer. A typical nucleosome carries 200 bp of the DNA helix. Nucleosomes repeat along the chromatin and look like ‘beads-on-string’ under the electron microscope.
NCERT Extract:
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). A typical nucleosome contains 200 bp of DNA helix. Nucleosomes constitute the repeating unit of a structure in nucleus called chromatin, thread-like stained (coloured) bodies seen in nucleus.”