You isolate nuclei from three different eukaryotic species. Youtreat the samples in exactly the same way (adding same amount ofenzyme, buffer and time) to partially digest the chromatin withmicrococcal nuclease, extract the DNA, and run it on a gel. You seethe 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 samewhat is your explanation for the difference in size in the patternsyou observe (shown below):
b- 2pts) If you digested each of the three samples morethoroughly, what would the pattern look like? [Be specific andindicate what the size of the bands would be]
c-3pt) An explorer discovers a strange newspecies of plant and sends some of the plant tissue to a geneticistto study. The geneticist performs the kinds of experiments asdescribed above in (b) except that: After digestion with nuclease120-bp fragment of DNA are seen.
Analysis of the histone core reveals histones in the followingproportions:
H2A 33.3%
H2B 33.3%
H3 0% [no histone H3 found]
H4 33.3%
On the basis of these observations, what conclusions could thegeneticist make about the probable structure of the nucleosome inthe chromatin of this plant? Be specific in describing the natureof the nucleosome: which histones form the core (1pt), how many ofeach 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 whenhistones were extracted from all of the chromatin (not just thenucleosome). What do you think the role of the new histone H7 wouldbe in this new plant species?
