Which temperature is used in the heat shock step to force bacterial cells to take up recombinant DNA?
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → 42°C
Bacterial cells take up recombinant DNA only after they are made competent. The final push is a heat shock: a short, sudden rise in temperature to 42°C between two spells on ice. The book prints this as 420C.
NCERT Extract:
Competent Host (For Transformation with Recombinant DNA) – “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. Recombinant DNA can then be forced into such cells by incubating the cells with recombinant DNA on ice, followed by placing them briefly at 420C (heat shock), and then putting them back on ice. This enables the bacteria to take up the recombinant DNA.”