Question

Which histone protein is not a part of histone octamer?
A. ${{H}_{2}}A$
B. ${{H}_{3}}$
C. ${{H}_{1}}$
D. ${{H}_{4}}$

Answer 1

Histone octamer can be defined as an eight-protein complex that is found at the center of the nucleosome. Histone proteins are the major proteins in chromatin. They regulate the function of the packaging of the DNA.

Complete answer:
The structure of DNA is coiled helical in shape which consists of two polynucleotide chains. DNA possesses the genetic instruction for the functioning, development, reproduction, and growth of all known organisms and also many viruses. Therefore, DNA is known as the genetic material of an organism. Chromatin is a complex macromolecule that makes up a chromosome that consists of DNA and protein. A complex made up of DNA and protein called chromatin is found in the cells of eukaryotic organisms. Nucleosomes are formed by wrapping DNA around histone proteins and a structure called beads on a string is formed. This structure is called euchromatin. A histone octamer is formed due to the assembly of tetramers with two copies of both ${{H}_{3}}$ and ${{H}_{4}}$, complexes with two ${{H}_{2}}A$/${{H}_{2}}B$complexes. The long DNA molecule is wrapped around these eight histones proteins and connects with the ${{H}_{1}}$ histone protein. ${{H}_{1}}$protein does not form part of the histone octamer.
Therefore, option C: ${{H}_{1}}$ is the correct answer.

Note: Histone proteins are abundantly found in lysine and arginine amino acids. These amino acids are positively charged which allow them to associate with DNA which is a negatively charged molecule. Thus, the packaging is tight due to the cancellation of the charges. The nucleosome arrays in their most compact form consist of multiple histones wrapped into a 30-nanometer fiber. This structure is called heterochromatin.