Two teams of researchers (I and II) extracted chromatin from nuclei and examined them with an electron microscope. Team I found that isolated chromatin resembles beads on a string. In contrast, Team II found that isolated chromatin appears as a condensed fiber of 30 nm in diameter.

Given below are a few reasons for these different outcomes:

A. Team I isolated the chromatin with low-ionic-strength buffer, and Team II isolated chromatin with an ionic strength of ~0.15M KCl (physiological ionic strength).
B. Team I isolated the chromatin with ~0.15M KCl and Team II did it with a low-ionic-strength buffer.
C. For Team II, the nuclear isolation method was not appropriate, and they had contamination from the cytoplasmic pool, leading to the appearance of the chromatin as a condensed fiber.
D. Team I chromatin got sheared during isolation, thus giving the appearance of beads on a string.

Among the statements given above, which statement/s most appropriately defines the divergent outcomes of Team I and Team II?

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Correct option is A

The correct answer is: 1. A only

Explanation :The difference in the outcomes of the experiments between Team I and Team II is largely influenced by the ionic strength of the buffer used in chromatin isolation.

• Statement A is correct: Team I isolated the chromatin with a low-ionic-strength buffer, while Team II used an ionic strength of ~0.15M KCl (physiological ionic strength). The low ionic strength used by Team I prevents the chromatin from remaining condensed, resulting in the "beads on a string" appearance. In contrast, the physiological ionic strength used by Team II maintains the chromatin in its more condensed state, leading to the appearance of a 30 nm condensed fiber.

• Statement B is incorrect: The ionic strength in Statement B is reversed for the two teams compared to the actual experimental setup.

• Statement C is incorrect: Although contamination can affect results, the most likely reason for the differences in the appearance of the chromatin is the difference in ionic strength rather than contamination from the cytoplasmic pool.

• Statement D is incorrect: Shearing of Team I chromatin during isolation would cause the chromatin to break into smaller fragments, giving it the beads-on-a-string appearance. However, Statement A alone is sufficient to explain the difference between the two teams, so Statement D is not the defining cause.

Information Booster:

1. Low-ionic-strength buffers destabilize chromatin structure, leading to the beads-on-a-string appearance.

2. Physiological ionic strength (~0.15M KCl) maintains the chromatin's condensed structure, which results in the 30 nm fiber.

3. The ionic strength directly affects the degree of chromatin condensation and its observable structure.

4. Chromatin in Team I remained less condensed because of the low ionic strength, creating a "beads on a string" form.

5. The chromatin appearance is influenced by the ionic strength used during isolation, affecting the structure observed under an electron microscope.

6. The difference in ionic strength explains the contrasting appearance of chromatin between the two teams.