Question

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?

Answer 1

Answer:

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.