Question

A 'beads on a string' like chromatin with 200 beads or nucleosomes, contains _______ bps of DNA.

• A. 80,000
• B. 40,000
• C. 20,000
• D. 10,000

Answer 1

Answer: (B)

40,000

Nucleosomes are fundamental organizational units of chromatin which appear as “beads-on-a-string” arrangement. Each bead of nuclesome has 200 bp of DNA which is wound 1.65 times around histone octamer. The bead plus linker DNA (20-40 bp; average 18 bp) leads to the next bead and form the nucleosomes. Therefore, a “beads on string” structure with 200 beads contains 218 X 200= 43600 bp DNA on an average.
This makes option B correct answer.