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Question #47740
The Question
During the preparation of competent bacterial cells for transformation, both chemical and physical treatments are employed to facilitate the uptake of hydrophilic recombinant DNA. Which of the following statements INCORRECTLY describes the mechanistic role of these treatments?
Options
- A.
Treatment with a specific concentration of Ca2+ increases the efficiency with which DNA enters the bacterium through pores in its cell wall.
- B.
The initial incubation of cells and DNA on ice neutralizes the electrostatic repulsion between the negatively charged DNA phosphate backbone and the bacterial surface.
- C.
A brief heat shock at 42°C induces a transient physical phase transition in the lipid bilayer, allowing the recombinant DNA to be forced into the cell.
- D.
Returning the cells to ice immediately after the heat shock decreases membrane fluidity, restoring structural integrity and trapping the plasmid inside.
Check Your Answer
Correct Answer
Step-by-Step Solution
Explanation
How the Examiner Thinks
Evolutionary_Exception
Tackle problems where standard rules evolve or change based on specific environmental constraints.
Concepts Behind This Question
Ethidium Bromide Visualization|Meselson-Stahl Density Gradient|Transcriptional Unit Boundaries
Why This Question Is Tricky
Common Mistakes
Conceptual Pivot: Students often memorize the transformation sequence (Calcium -> Ice -> Heat Shock -> Ice) without mapping the specific biophysical function to the correct step.
This question uses a 'Functional Confusion' trap by shifting the chemical function (charge neutralization by Ca2+) to a physical step (incubation on ice).
Quick Facts About This Question
Question Information
| Subject | Biology |
| Chapter | Biotechnology : Principles and Processes - Class 12 |
| Concept | Ethidium Bromide Visualization |
| Difficulty | 8 |
| Cognitive Load | 5 |
| Target Solve Time | 120 sec |
| Access | Free |