Question

Significance of treating bacterial cells with calcium chloride before transformation is to facilitate

• A. binding of DNA to the cell surface
• B. uptake of DNA through membrane transport proteins
• C. uptake of DNA by creating transient pores in the bacterial cell wall
• D. expression of antibiotic resistance gene

Answer 1

The correct option is A binding of DNA to the cell surface

Since DNA is a hydrophilic molecule, it cannot pass through cell membranes. In order to force bacteria to take up the plasmid, the bacterial cells must first be made 'competent' to take up DNA. This is done by treating them with a specific concentration of a divalent cation, such as calcium, which increases the efficiency with which DNA enters the bacterium through pores in its cell wall. Possibly, calcium chloride causes the DNA to precipitate onto the outside of the cells or it may improve DNA binding.