Question

In tertiary structure of DNA, what is a histone octamer?

• A. A complex consisting of eight positively charged histone proteins (two of each $H_{2}A,H_{2}B,H_3$ and $H_4$ ) that aid in the packaging of DNA.
• B. A complex consisting of eight negatively charged histone proteins (two of each $H_{2}A,H_{2}B,H_3$ and $H_4$ ) that aid in the packaging of DNA.
• C. A complex consisting of nine positively charged histone proteins $(H_1$ and two of each $H_{2}A,H_{2}B,H_3$ and $H_4$ ) that aid in the packaging DNA.
• D. A complex consisting of nine negatively charged histone proteins $(H_1$ and two of each $H_{2}A,H_{2}B,H_3$ and $H_4$ ) that aid in the packaging of DNA.

Answer 1

Answer: (A)

A histone octamer is a complex of eight positively charged histone proteins (two of each $H_{2}A,H_{2}B,H_3$ and $H_4$ ) that aid in the packaging of DNA. Negatively charged DNA wraps around these histone octamers to form the nucleosome. The DNA is held there by ionic bonds. Linker histone $H_1$ binds to each nucleosome where the DNA enters and exits and this draws a string of nucleosomes closer together to form the $10nm$ fibre. The nucleosomes in chromatin are seen as beads-on string structure when viewed under electron microscope.