Question

Nucleosome a repeating structural unit within eukaryotic chromatin is made up of

• A. 140 bp of DNA making 1.65 negative super helical turn wrapped around a hexamer of histones
• B. 146 bp of DNA making 1.65 negative super helical turn wrapped around a dimer of histones
• C. 140 bp of DNA making 1.65 negative super helical turn wrapped around an octamer of histones
• D. 146 bp of DNA making 1.65 negative super helical turn wrapped around an octamer of histones

Hint:

• Nucleosome Core Particle
  • DNA: ~146-147 bp wrapped ~1.65 times.
  • Histone Octamer: 2x(H2A + H2B + H3 + H4).
• Histone H1 (linker histone) binds to linker DNA and helps compact nucleosomes further.
• This "beads-on-a-string" structure is the first level of chromatin organization.

Answer 1

The Correct Option is D

The nucleosome is a fundamental unit of chromatin in eukaryotic cells, responsible for the packaging of DNA into a more compact structure. It consists of a segment of DNA wrapped around a core of histone proteins.

In the context of the given options, the correct structure of a nucleosome includes:

• 146 base pairs (bp) of DNA: This DNA makes approximately 1.65 negative super helical turns around the histone core.
• Histone Octamer: The core particle of the nucleosome consists of eight histone proteins, forming an octamer. Typically, this includes two molecules each of histones H2A, H2B, H3, and H4.

Therefore, the correct statement of a nucleosome structure is:

146 bp of DNA making 1.65 negative super helical turn wrapped around an octamer of histones