The correct sequence of making a cell competent is

Options

A. 1. treatment with divalent cation `rarr` incubation of cells with recombinant `DNA` of ice `rarr` heat shock `(42^(@)C)rarr` placing on ice
B. 2. heat shock `(42^(@)C)rarr` incubation of cells with recombinant DNA on ice `rarr` treatment with divalent cations `rarr` placing on ice
C. 3. treatment with divalent cation `rarr` placing on ice `rarr` incubation of cells with recombinant DNA on ice `rarr` heat shock `(42^(@)C)`
D. 4. incubation of cells with recombinant DNA on ice `rarr` heat shock `(42^(@)C) rarr `treatment with divalent cations `rarr` placing on ice.

Answer

To determine the correct sequence of making a cell competent for DNA uptake, we follow these steps:

### Step-by-Step Solution:

1. **Treatment with Divalent Cations**:
- The first step involves treating the cells with divalent cations, such as calcium ions. This treatment helps to destabilize the cell membrane, making it more permeable and allowing for easier uptake of DNA.

2. **Incubation with Recombinant DNA on Ice**:
- After the treatment with divalent cations, the cells are incubated with the recombinant DNA on ice. This step allows the DNA to bind to the surface of the cells without causing any immediate uptake, as the low temperature slows down cellular processes.

3. **Heat Shock at 42°C**:
- The next step is to subject the cells to a heat shock at 42°C. This sudden increase in temperature creates pores in the cell membrane, facilitating the entry of the recombinant DNA into the cells.

4. **Placing on Ice**:
- Finally, the cells are placed back on ice. This cooling step helps to stabilize the cells and allows the DNA to be incorporated into the cells without complications.

### Conclusion:
The correct sequence of making a cell competent is:
- Treatment with divalent cations
- Incubation of cells with recombinant DNA on ice
- Heat shock at 42°C
- Placing on ice

Thus, the correct answer is **Option 1**.

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