Arrange the steps for transformation of recombinant DNA in sequence -

(A). For heat shock, bacterial cells are placed at 42°C; and then they are placed on ice.

(B). The bacterial cells must be made 'competent' to take up DNA by treating them with a specific concentration of divalent cation such as calcium.

(C). The bacteria are now able to take up the recombinant DNA.

(D). Recombinant DNA can then be forced into those cells by incubating the cells with recombinant DNA on ice.

Choose the correct answer from the options given below:

(B), (D), (A), (C)

The correct answer is Option (1) - (B), (D), (A), (C)

(B). The bacterial cells must be made 'competent' to take up DNA by treating them with a specific concentration of divalent cation such as calcium.

(D). Recombinant DNA can then be forced into those cells by incubating the cells with recombinant DNA on ice.

(A). For heat shock, bacterial cells are placed at 42°C; and then they are placed on ice.

(C). The bacteria are now able to take up the 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.

The transformed bacterial cells are plated on an agar medium containing an antibiotic. Only the cells that have successfully taken up and expressed the antibiotic resistance gene (often included in the rDNA) will survive and grow, allowing for the selection of transformed colonies.