You perform an experiment in which chromatin is isolated from sea urchin sperm c

Question

You perform an experiment in which chromatin is isolated from sea urchin sperm cells and briefly digested with micrococcal nuclease. When chromatin proteins are removed and the resulting purified DNA is analyzed by gel electrophoresis, you observe a series of DNA fragments that are multiples of 260bp in length. a. What can you conclude about the amount of DNA that is associated with each nucleosome? b. Suppose you perform an experiment in which chromatin is digested for a much longer period of time with mictacoccal nuclease before the removal of chromatin proteins. When the resulting DNA preparation is analyzed by gel electrophoresis, all of the DNA appears as fragments 146bp in length What does this suggest to you about the length of linker DNA?

Explanation / Answer

1. Nucleosome: it is a beed like structure ine which DNA will be wrapped around an octameric protein.

So the wrapped DNA is 260 bp in length.

So the length of DNA is 260 base pair which is associated with nucleosome.

b. The linker DNA have length of= 260-146= 14 bp.

so the linker DNA is 14 bp.

the nucleosome structure appears as bead on string. The bead on string model is given for the structure of nucleosome in which bead like structures are present in a long thread. These structures are considered as nucleosome and the long thread between the beats are considered as linker DNA.

So when we cut the DNA by small exposure of enzymes than nucleosome plus linker DNA fragment is appeared which is 260 base pair and length.

when nucleosome and linker DNA is separated then 146 base pair is covered by the DNA around histone and 14 base pairs is appeared as linker DNA.

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