Heat Shock Transformation of Bacteria — NEET Biology
📚 Practice ConceptRecombinant DNA can then be forced into such cells by incubating the cells with recombinant DNA on ice, followed by placing them briefly at 42°C (heat shock), and then putting them back on ice. This enables the bacteria to take up the recombinant DNA.
Arrange the following steps in the correct chronological order for making bacterial cells competent and facilitating the uptake of recombinant DNA. I. Incubation of cells with recombinant DNA on ice. II. Treatment of bacterial cells with a specific concentration of a divalent cation like calcium. III. Briefly placing the cells at 42°C (heat shock). IV. Transferring the cells back to ice. V. Introduction of recombinant DNA into the surrounding medium of the cells.
View solution & NCERT explanation
Correct answer: A — II → V → I → III → IV
The core concept involves the sequence of steps to prepare competent host cells and induce them to take up recombinant DNA. 1. **II. Treatment of bacterial cells with a specific concentration of a divalent cation like calcium.** NCERT states: "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..." 2. **V. Introduction of recombinant DNA into the surrounding medium of the cells.** The recombinant DNA must be present for the cells to take it up. 3. **I. Incubation of cells with recombinant DNA on ice.** NCERT states: "Recombinant DNA can then be forced into such cells by incubating the cells with recombinant DNA on ice...". This step comes after making cells competent and adding DNA. 4. **III. Briefly placing the cells at 42°C (heat shock).** NCERT states: "...followed by placing them briefly at 42°C (heat shock)." 5. **IV. Transferring the cells back to ice.** NCERT states: "...and then putting them back on ice. This enables the bacteria to take up the recombinant DNA." The correct chronological order is II → V → I → III → IV. Option A correctly represents this sequence. Options B, C, and D present incorrect sequences that do not follow the established procedure described in NCERT. This question assesses the understanding of the practical steps involved in transformation of bacterial cells.
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