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

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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.

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.

A complex consisting of nine positively charged histone proteins (H₁ and two of each $H_{2} A, H_{2} B, H_{3} and H_{4}$ ) that aid in the packaging DNA.

A complex consisting of nine negatively charged histone proteins (H1 and two of each $H_{2} A, H_{2} B, H_{3} and H_{4}$ ) that aid in the packaging of DNA.

answer is A.

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Detailed Solution

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 H₁ binds to each nucleosome where the DNA enters and exits and this draws a string of nucleosomes closer together to form the 10 nm fibre. The nucleosomes in chromatin are seen as beads-on string structure when viewed under electron microscope.