Try it on paper first. A hint, the key idea and the worked solution are here when you need them.
The DNA of a nucleosome is base pairs long when stretched out. The bead of a nucleosome is about across. A human cell has nucleosomes.
Have you tried it?
Work it out on paper first. It is fine to get stuck or make a mistake: that is how we learn. When you are ready, go through the solution one step at a time, and check each step against your own.
Given. base pairs, a bead of , and nucleosomes.
Plan. Find the length of the DNA of one bead, divide by the bead, then multiply by the number of beads.
Step 1. (a) .
Step 2. (b) . The DNA becomes about six times shorter.
Step 3. (c) , which is .
Step 4. (d) No. A line of is still about times longer than a nucleus a few micrometres wide. The chromatin fibre and the chromosome fold it much further, with the help of the NHC proteins.
Answer: ; ; ; no.
Check. The packing ratio is also .
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A nucleosome has about 200 base pairs of DNA round a core of 8 histone molecules. The helix has 10 base pairs in one turn, in the textbook model.
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