Question

Explain how is a bacterial cell made ’competent’ to take up recombinant DNA from the medium.

Hint:

In PCR, each cycle doubles the amount of DNA, leading to exponential amplification. The key to success in PCR is using a heat-stable polymerase enzyme like Taq polymerase.

Answer 1

Making Bacterial Cells Competent for DNA Uptake 

Bacterial cells can be made competent to take up recombinant DNA using two major methods:

1. Chemical Transformation

• Bacterial cells are treated with calcium chloride: \[ \text{CaCl}_2 \]
• This treatment increases the permeability of the bacterial cell membrane.
• The recombinant DNA can then pass through the cell membrane more easily.

2. Electroporation

• An electrical pulse is applied to the bacterial suspension.
• This creates temporary pores in the bacterial membrane.
• DNA molecules enter the cell through these pores.

3. Selection

• After transformation, bacterial cells are incubated on selective media.
• Only those cells that have successfully taken up the recombinant DNA will survive and grow.