Question

Histone octamer contains
A. Eight types of histones
B. Eight histones of four different types
C. Five histones
D. Six types of histones

Answer 1

The histone octamers are found in the DNA. The DNA stands for Deoxyribonucleic acid. It is the genetic material of all eukaryotic organisms. Moreover, the DNA has a double helical, spirally coiled structure.

Complete answer: The packaging of the DNA in eukaryotic organisms is very complex. The packaging is done with the help of histones. Histones are a set of positively charged basic proteins. These proteins are rich in basic amino acid residues like lysines and arginines. Along with this, they have the charged side chains present. Histone proteins are of five different types. These five types are ${H_1},{H_2}A,{H_2}B,{H_3}$ and ${H_4}$. Out of these five types, four histone proteins occur in pairs to form the histone octamer or the nu-body. These four histone proteins that occur in pairs are ${H_2}A,{H_2}B,{H_3}$ and ${H_4}$. The positively charged histone octamer has the negatively charged DNA wrapped around it. Together they form a structure known as the nucleosome. The remaining histone protein is attached to the DNA. Thus, based on the above information we can conclude that the Histone octamer contains eight histones of four different types.
Hence, the correct answer is option B.

Note: Approximately 200 base pairs of DNAs are wrapped around the nu-body to complete about one full and a three-quarter turn. The DNA, i.e. present between two adjacent nucleosomes is known as the linker DNA. The nucleosome constitutes the repeating units of a structure in the nucleus that is called the chromatin. This chromatin gives the ‘beads on string’ appearance to the DNA under the electron microscope.