Correct option is A
Explanation-
Statement A:"The histone tetramer in the core of the nucleosome comprises H2A, H2B, H3 and H4." - INCORRECT
The nucleosome core particle consists of:
1. Histone octamer: 2 copies each of H2A, H2B, H3, and H4.
2. The tetramer part refers specifically to (H3–H4)₂ — a central tetramer. H2A and H2B form dimers, not part of the tetramer.
So, statement A misrepresents the tetramer composition.
Statement B: "The N-terminal tails of the core histones are believed to stabilize the 30 nm fiber of nucleosomal DNA by their interactions with adjacent nucleosomes." - CORRECT
The positively charged N-terminal tails of histones extend outward from the nucleosome and interact with adjacent nucleosomes, linker DNA, scaffold proteins. These interactions help stabilize higher-order chromatin structure (like the 30 nm fiber).
Statement C: "The post-translational modifications of the N-terminal tails as well as globular domains of the core histones modulate transcriptional events." - CORRECT
Histone tails undergo modifications - acetylation, methylation, phosphorylation, ubiquitination. These influence chromatin compaction and gene expression. Even globular domains (e.g., H3-K56 acetylation) affect chromatin accessibility.
Statement D: "According to the zigzag model of the 30 nm fiber the linker DNA circles around the central axis of the fiber as the DNA moves from one nucleosome to the next." - INCORRECT
In the zigzag model of 30 nm chromatin , nucleosomes are arranged in a zigzag pattern with straight linker DNA connecting alternate nucleosomes. The linker DNA does not spiral around the central axis — this description fits the solenoid model, not the zigzag model.
Final Answer: Statements B and C are correct → Option a
