Question

How many nucleosomes are found in a helical coil of 30 nm chromatin fibre
a. 10
b. 12
c. 06
d. 09

Answer 1

Hint: In the DNA packaging of eukaryotes, nucleosomes play an important role. It is the fundamental subunit of chromatin. Each nucleosome consists of two or fewer turns of DNA helix where up to eight proteins are present as beads on the chromatin strand. These eight proteins present on the string of chromatids are known as histone octamers.

Complete answer:
The form of the nucleosome is more or much less a flat cylinder and the ten nm fibre is fashioned by way of stacking of the nucleosomes. The nucleosomes are tilted at an attitude of 20° to the fibre axis. Coiling of the 10 nm fibre occurs inside the presence of HI histone to offer upward thrust to a 30 nm fibre.
> The number of nucleosomes consistent with flip within the 30 nm fibre is 6 which have a radial business enterprise, this is referred to as the solenoid model of chromatin structure. The coiling of nucleosomes is sort of a helix wherein the perspective of flip between the faces of nucleosomes is 60°
> DNA is associated with histones to shape nucleosome particles. One nucleosome contains two hundred bp DNA (67 nm long). Its paperwork is 10 nm in diameter. The diameter of the nucleosome is eleven nm and thus the packing ratio of DNA is sixty-seven/eleven or approximately 6.
> Coiling of 10 nm fibre takes place to form the chromatin fibre of about 30 nm diameter. It includes 6 nucleosomes according to the turn of the coil, accordingly making the DNA packing ratio of approximately forty.
> The folding of 30 nm fibre offers upward thrust to a packing ratio of approximately one thousand in euchromatin.

Hence, the correct answer is option (C).

Note: The nucleosome is made with the aid of winding the DNA around eight histone protein cores. There are five varieties of histone proteins, H1, H2A, H2B, H3, and H4. Four of them (H2A, H2B, H3, and H4) get up in pairs to supply histone octamers, known as a nu body or center of the nucleosome. H1 protein is answerable for linking octamers.