Arrange the following steps for making the bacterial cell competent to take up DNA, in chromonological order .
I. Incubation of cells with recombinant DNA on ice.
II . Incubation of cells with recombinant DNA at 42 degree Celsius.
III. Treating cells with a specific concentration of a divalent cation such as calcium .

Options

A. III followed by II followed by I followed by II
B. III followed by I followed by II followed by I
C. I followed by II followed by III followed by II
D. II followed by I followed by III followed by I

Answer

To arrange the steps for making a bacterial cell competent to take up DNA in chronological order, we need to understand the process involved in transforming bacterial cells. Here’s the step-by-step solution:

### Step-by-Step Solution:

1. **Treating cells with a specific concentration of a divalent cation such as calcium.**
This step is essential as divalent cations like calcium ions help to neutralize the negative charges on the DNA and the bacterial cell membrane, facilitating the uptake of DNA.

2. **Incubation of cells with recombinant DNA on ice.**
After treating the cells with calcium, the next step is to incubate them with recombinant DNA on ice. This low temperature helps to stabilize the DNA and the cells, allowing for better interaction.

3. **Incubation of cells with recombinant DNA at 42 degrees Celsius.**
Finally, the cells are subjected to a heat shock at 42 degrees Celsius. This heat shock creates a thermal imbalance that encourages the DNA to enter the bacterial cells.

### Chronological Order:
- III (Treating cells with a specific concentration of a divalent cation such as calcium)
- I (Incubation of cells with recombinant DNA on ice)
- II (Incubation of cells with recombinant DNA at 42 degrees Celsius)

### Final Answer:
The correct chronological order is: **III → I → II**

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