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 \[{{H}_{2}}B,\]\[{{H}_{3}}\]and\[{{H}_{4}}\]) that aid in the packaging of DNA.
Correct Answer: A
Solution :
[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 10 nm fibre. The nucleosomes in chromatin are seen as beads-on string structure when viewed under electron microscope.
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