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 follow the correct sequence of the procedures involved. 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 is the first step. The divalent cation, typically calcium ions, helps to create pores in the bacterial cell wall, making it more permeable to DNA.

2. **Incubation of cells with recombinant DNA on ice.**
- After the cells have been treated with calcium, they are incubated with recombinant DNA on ice. This step helps to maintain the permeability of the bacterial cells, allowing the DNA to enter more easily.

3. **Incubation of cells with recombinant DNA at 42 degrees Celsius.**
- The final step involves applying a heat shock at 42 degrees Celsius. This sudden increase in temperature facilitates the uptake of DNA by the bacteria through the pores created earlier.

### Chronological Order:
The correct chronological order of the steps is:
1. III - Treating cells with a specific concentration of a divalent cation such as calcium.
2. I - Incubation of cells with recombinant DNA on ice.
3. II - Incubation of cells with recombinant DNA at 42 degrees Celsius.