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 introducing recombinant DNA into bacterial cells. Here’s the step-by-step solution:

1. **Treatment of bacterial cell with divalent cations at 4°C**: 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 make the bacterial cell membrane more permeable, allowing DNA to enter the cells more easily.

2. **Heat shock (at 42°C)**: After the cells have been treated with divalent cations, the next step is to subject them to heat shock at a higher temperature (42°C). This sudden increase in temperature creates a thermal imbalance that facilitates the uptake of the recombinant DNA into the bacterial cells.

3. **Bacterial cells are incubated with recombinant DNA on ice**: Following the heat shock, the cells are placed on ice. This step helps to stabilize the cells and allows the recombinant DNA to associate with the cells before they are allowed to recover at a warmer temperature.

4. **Recombinant/Transformed bacteria are plated and kept at 37°C**: Finally, the transformed bacteria 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.