Question

During the process of making bacteria competent for recombinant DNA technology, which treatment is commonly used?

• A. Treatment with calcium chloride
• B. Treatment with sodium hydroxide
• C. Treatment with ethanol
• D. Treatment with glucose solution

Hint:

Remember: Competent cells in recombinant DNA technology are usually prepared using chilled \( CaCl_2 \) followed by heat shock.

Answer 1

The Correct Option is A

Concept: Competent bacterial cells are cells capable of taking up foreign DNA from the surrounding medium.

Step 1: Understanding competency.
Normally, bacterial cell membranes repel negatively charged DNA molecules due to the presence of negatively charged phospholipids.

Step 2: Role of calcium chloride.
Cells are treated with chilled calcium chloride solution because:

• Calcium ions neutralize negative charges.
• Cell membrane permeability increases.
• DNA uptake becomes easier.

Step 3: Heat shock process.
After calcium chloride treatment, cells are briefly exposed to higher temperature (heat shock), allowing plasmid DNA to enter the bacterial cell.

Step 4: Selecting the correct option.
Hence, calcium chloride treatment is used to make bacteria competent.