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:
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → (B), (D), (A), (C)
(B) Making the cells competent — first. DNA is a hydrophilic molecule and cannot pass through cell membranes. Calcium treatment makes the bacterial cells able to take up DNA.
(D) Incubating the cells with recombinant DNA on ice — second. The competent cells and the recombinant DNA are kept together in the cold, so that the DNA sits close to the cells.
(A) Heat shock at 42°C, then back on ice — third. The short heat shock pushes the DNA into the cells through the pores in the cell wall.
(C) The bacteria take up the recombinant DNA — last. This is the result of the steps before it: the host is now transformed and carries the recombinant DNA.
NCERT Extract:
Cloning Vectors – …
