Question

The given figure shows the structure of a nucleosome with its parts labelled as A, B & C. Identify A, B and C.

• A. A – Histone octamer; B – RNA; C – H1 histone
• B. A – RNA; B – H1 histone; C – Histone octamer.
• C. A – DNA; B – H1 histone; C – Histone octamer
• D. A – H1 histone; B – DNA; C – Histone octamer

Answer 1

The correct option is C A – DNA; B – H1 histone; C – Histone octamer

DNA
The given diagram represents a nucleosome. DNA is negatively charged and wraps around positively charged histone octamer in 2 circles to stabilise the charge. Approximately, 200bp of DNA wrap around one histone octamer. Part ‘A’ represents the DNA.

H1 Histone
The H1 histone is the linker histone. It binds to a part of the linker DNA that connects the adjacent nucleosomes. Linker DNA in association with histone H1, holds the cores together. Part ‘B’ represents the H1 histone molecule.


Histone octamer
Histones are positively charged proteins rich in basic amino acids such as lysine and arginine. 8 histone proteins (2 molecules each of H2A, H2B, H3 and H4) form an octamer that forms the core of the nucleosome structure. Hence, part ‘C’ here represents the histone octamer.

Final answer

(A) A – DNA; B – H1 histone; C – Histone octamer