Question

You perform an experiment in which chromatin is isolated from sea urchin sperm cells and briefly digested with micrococcal nuclease. When the 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 260 base pairs in length (that is, 260 bp, 520 bp, 780 bp, and so forth). a) Although these results differ somewhat from the typical results discussed in the chapter, explain why they still point to the likely existence of nucleosomes in this cell type. b) What can you conclude about the amount of DNA that is associated with each nucleosome

Answer 1

Answer:

a) DNA fragments associated with histone proteins are all multiple in length (i.e., 260 bp, 520 bp, 780 bp, etc), thereby suggesting the presence of a pattern of organization in the chromatin  

b) it suggests that each unit of organization (ie, each nucleosome) consists of 260 bp associated with chromatin proteins

Explanation:

The nucleosome is considered as the basic unit of chromatin. A nucleosome consists of approximately two turns of DNA wrapped around a core of eight histone proteins (i.e., a histone octamer). The histone octamer consists of two copies of each of the histones H2A, H2B, H3, and H4. Moreover, the nucleosomes are connected together by linker DNA sequences which vary between 10 and 100 bp in length.