Question

Number of histone proteins in each nucleosome core is
A) 8
B) 10
C) 12
D) 14

Answer 1

Histones are highly basic proteins found in eukaryotic cell nuclei that pack and order the DNA into structural units called nucleosomes.

Complete Answer:

1. A nucleosome consists of a segment of DNA wound around a core (“octamer”) of 8 histone proteins (two each of histones H2A, H2B, H3, and H4). So the number of histone proteins in each nucleosome core '8'.
2. Nucleosomes constitute the basic repeating subunit of chromatin. Each nucleosome can be considered as composed of a nucleosome ‘core’, linker DNA, and in most instances, a linker histone. We will first consider the components and structure of the nucleosome core, and then the linker DNA and linker histone.
3. The core DNA is in tight association with the core histones and is protected from nuclease digestion whereas the linker DNA is rapidly digested. Indeed the term “nucleosome core particle” was originally defined as the product of extensive micrococcal nuclease digestion of native chromatin.

Hence, the correct answer is option A (8).

Additional information: The four core histones are relatively small (11-15 kDa), very basic proteins that are highly conserved among eukaryotic species. About 25% of the mass of each core histone is contained within an N-terminal ‘tail’ domain that is unstructured in the absence of DNA or other macromolecular interactions

Note: Eukaryotic chromatin is a complex and dynamic system in which the DNA double helix is organized and protected by interactions with histone proteins. This system is regulated through a large network of dynamic post-translational modifications (PTMs) which ensure proper gene transcription, DNA repair, and other processes involving DNA.