Question

In order to force bacteria to take up the recombinant DNA, they must be made competent. Explain how it can be achieved.

Hint:

Chemical transformation with calcium chloride and heat shock are common methods for making bacteria competent to take up recombinant DNA.

Answer 1

Step 1: Chemical Transformation.
Bacteria can be made competent by treating them with a solution of calcium chloride (CaCl₂), which makes their cell membrane more permeable to DNA.
Step 2: Heat Shock Treatment.
After incubation with calcium chloride, the bacteria are subjected to a heat shock at 42°C for a brief period. This creates a temperature gradient that drives the DNA into the bacterial cells.
Step 3: Recovery and Selection.
After the heat shock, the bacteria are allowed to recover in a nutrient medium. Then, they can be grown on selective media to isolate those that have successfully taken up the recombinant DNA.