Given below are different steps of transformation in a bacterial cell. Arrange them in correct sequence. (i) Heat shock (at 42°C) (ii) Treatment of bacterial cell with divalent cations at 4°C (iii) Bacterial cells are incubated with recombinant DNA on ice (iv) Recombinant/Transformed bacteria are plated and kept at 37°C

Options

A. (i), (ii), (iii), (iv)
B. (ii), (i), (iii), (iv)
C. (ii), (iv), (i), (iii)
D. (iv), (ii), (iii), (i)

Answer

To arrange the steps of transformation in a bacterial cell in the correct sequence, we need to understand the process of making bacterial cells competent to take up recombinant DNA. Here’s the step-by-step solution:

1. **Treatment of bacterial cell with divalent cations at 4°C (Step ii)**: The first step involves treating the bacterial cells with divalent cations, such as calcium ions, at a low temperature (4°C). This treatment helps to stabilize the cell membrane and makes the cells more permeable, allowing them to take up DNA more easily.

2. **Heat shock (at 42°C) (Step i)**: After the treatment with divalent cations, the bacterial cells undergo a heat shock at 42°C. This sudden increase in temperature creates a thermal imbalance that facilitates the uptake of DNA into the bacterial cells through the pores created in the cell membrane.

3. **Bacterial cells are incubated with recombinant DNA on ice (Step iii)**: Following the heat shock, the cells are incubated with recombinant DNA on ice. This step allows the DNA to associate with the competent cells and helps stabilize the DNA within the cells.

4. **Recombinant/Transformed bacteria are plated and kept at 37°C (Step iv)**: Finally, the transformed bacteria, which have taken up the recombinant DNA, are plated on a growth medium and incubated at 37°C. This temperature is optimal for bacterial growth, allowing the transformed cells to multiply and express the recombinant DNA.

Thus, the correct sequence of steps is:
(ii) Treatment of bacterial cell with divalent cations at 4°C → (i) Heat shock (at 42°C) → (iii) Bacterial cells are incubated with recombinant DNA on ice → (iv) Recombinant/Transformed bacteria are plated and kept at 37°C.

**Final Sequence**: ii → i → iii → iv