Question

Unusual eukaryotic-like (possessing a defined nucleus) cells were obtained from a sample of water from a subglacial antarctic lake. To investigate the properties of the new organism's genome, the nucleus was carefully isolated and the chromatin obtained. The fibers had a "beads on a string" appearance, suggesting some type of "histones." Following digestion with micrococcal nuclease, protein removal, and gel electrophoresis, DNA fragments were obtained that are multiples of 280 base pairs in length. Longer incubation with micrococcal nuclease prior to protein removal results in fragments 200 base pairs in length. The amount of DNA that is wrapped around the "core histones" is therefore

A) 80 base pairs in length.
B) 200 base pairs in length.
C) 360 base pairs in length.
D) 480 base pairs in length.
E) Not enough information is given to determine the answer.

Answer 1

The amount of DNA wrapped around the core histones in a nucleosome is 200 base pairs in length, determined by micrococcal nuclease digestion and analysis of resulting DNA fragments.

Step-by-step explanation:

The length of DNA that is wrapped around the "core histones" in a nucleosome can be determined by understanding the digestion pattern of chromatin structures by micrococcal nuclease and subsequent DNA analysis. Initially, fragments are multiples of 280 base pairs in length, which likely includes the DNA wrapped around the nucleosome plus linker DNA. When micrococcal nuclease activity is prolonged, the resulting fragments are 200 base pairs long, suggesting the removal of the linker DNA, and this represents the length of DNA that wraps around the nucleosome core. Therefore, the answer is B) 200 base pairs in length. The difference between the initial fragment length (280 bp) and the core fragment length (200 bp) would represent the length of the linker DNA (280 bp - 200 bp = 80 bp), which is not the DNA length associated with the core histone proteins but rather the connecting segment between nucleosomes.