Question

You isolate nuclei from three different eukaryotic species. You treat the samples in exactly the same way (adding same amount of enzyme, buffer and time) to partially digest the chromatin with micrococcal nuclease, extract the DNA, and run it on a gel. You see the pattern below:

Lane	Approximate size of bands (in base pairs)
1	200, 400, 600, 800
2	180, 360, 540, 720
3	190, 380, 570, 760

a-2pts) Knowing that the core-DNA in all cell types is the same what is your explanation for the difference in size in the patterns you observe (shown below):

b- 2pts) If you digested each of the three samples more thoroughly, what would the pattern look like? [Be specific and indicate what the size of the bands would be]

c-3pt) An explorer discovers a strange new species of plant and sends some of the plant tissue to a geneticist to study. The geneticist performs the kinds of experiments as described above in (b) except that: After digestion with nuclease 120-bp fragment of DNA are seen.
Analysis of the histone core reveals histones in the following proportions:

H2A 33.3%
H2B 33.3%
H3 0% [no histone H3 found]

H4 33.3%

On the basis of these observations, what conclusions could the geneticist make about the probable structure of the nucleosome in the chromatin of this plant? Be specific in describing the nature of the nucleosome: which histones form the core (1pt), how many of each are in there (1pt) and how much core-DNA is around it (1pt).

d-2pt) The geneticist also found H1 and a new histone H7 when histones were extracted from all of the chromatin (not just the nucleosome). What do you think the role of the new histone H7 would be in this new plant species?

Answer 1

a)The difference in size of DNA banding pattern is due to micrococal Nuclease anomalous digestion pattern.The nucleosomes undergo exonucleolytic trimming by micrococal Nuclease causing anomalous pattern of ladder.

b)Throughly digestion of the sample with MNase cause removal of 50bp from end of each nuclei bands.

1-150,350,550,750

2-130,310,490,670

3-140,330,520,710

c)H2A-It packs DNA into chromatin by compacting thus giving it proper structure.The proper arrangement of DNA into chromatin fiber specifies gene expression and its regulation.It consist of high glycine ,leucine and low serinre.

H4-It take part in the structure of chromatin in the cell.And also take pat in the acetylation and methylation of the histone causing huge impact on gene expression.

H2B-It take part in the formation of nucleosome structure,i.e beads in the string form.Higher serine and low glycine and leucine.

H1-It is most conserved form of histone in nucleosomes.Take part in the proper arrangement of DNA wrapped around the histones placed on top the nucleosome structure.

d)H2A and H2B form dimer and H4 and H7 forms tetramer.The core consist of H24,H2B and H4.H1 and H7 LEADS The DNA.