Architecture of the nucleosome A canonical nucleosome particle is composed of which histone assembly together with approximately how much DNA?

Introduction:
The nucleosome is the fundamental repeating unit of chromatin. Knowing its composition is essential for understanding DNA accessibility, transcription regulation, and higher order chromosome organization.

Given Data / Assumptions:

• Core histones are H2A, H2B, H3, and H4.
• DNA wraps around the histone surface in left handed superhelical turns.
• Linker DNA connects adjacent nucleosomes and varies in length beyond the core particle.

Concept / Approach:

The nucleosome core particle contains two copies of each core histone, forming an octamer. About 146 base pairs of DNA are tightly wrapped around this octamer in about 1.7 turns, creating a protected core resistant to nucleases relative to linker DNA.

Step-by-Step Solution:

Verification / Alternative check:

Micrococcal nuclease digestion yields a protected fragment of about 146 base pairs, a classic experimental signature of the nucleosome core particle.

Why Other Options Are Wrong:

Options listing tetramer or hexamer do not match the core octameric structure. Three hundred base pairs overstates the core wrapped DNA and confuses core with nucleosome plus long linker.

Common Pitfalls:

Assuming the protected length widely varies or that H1 is part of the core octamer. H1 is linker associated and not counted in the core particle composition.

Final Answer:

Histone octamer and about 146 base pairs of DNA