4-10 Assuming that the 30-nm chromatin fiber contains about 20 nucleosomes (200 bp/nucleosome) per 50 nm of length, calculate the degree of compaction of DNA associated with this level of chromatin structure. \A4rat fraction of the 10,000-fold condensation that occurs at mitosis does this level of DNA packing represent?

The degree of compaction of the 30nm (width) of chromatin fiber is 27 fold while this level of DNA packing represents only 0.27% of the total 10,000-fold condensed DNA.

Explanation:

width: 30 nm

length: 50 nm

1 nucleotide (base pair) has a length of 0.34nm

Degree of Compaction

If per 50 nanometers length of double-stranded DNA you have 20 nucleosomes (200 bp/nucleosome), then the degree of condensation would be: 20 nucleosomes x 200 bp/nucleosome x 0.34 nm/bp = 1360 nm

1360nm/50nm= 27.2.

The degree of compaction of the 30nm (width) of chromatin fiber is 27 fold.

Fraction of 10,000 fold condensation.

There are 6 levels of compaction (or condensation) of the DNA:

level 1, in which there is no condensation at all,

level 2, in which there is a 3 fold condensation (beads on a string),

level 3, in which there is a 27 fold condensation (30-nm of chromatin packed nucleosomes)

level 4, in which there is a 700 fold condensation,

level 5 with a 1,000 fold condensation (a condensed section of a chromosome),

level 6 with a 10,000 (net condensation of a DNA molecule in a chromosome during mitosis).

The fraction that the 27 fold condensation represents out of the final 10,000-fold condensation is

27/10,000 = 0.0027 or in percentage would be (27x100)/10,000 = 0.27 %, which means that this level of DNA packing represents only 0.27% of the total 10,000-fold condensed DNA.

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