Biology Biotechnology PMDC Conceptual Practice
PMDC Verified Question 8 of 65
Bacterial cells take up recombinant plasmids more efficiently when treated with:
A
Sodium chloride
B
Calcium chloride
C
Potassium chloride
D
Cesium chloride
Tap any option to test your recall and reveal the step-by-step Propolis autopsy.

Propolis Cognitive Error Autopsy

Official Correct Choice:
Option B: Calcium chloride
Concept:

Artificial competence induction for bacterial transformation.

Solution:

Treating bacterial cells with ice-cold calcium chloride (\( \text{CaCl}_2 \)) neutralizes the repulsive negative charges on both the plasmid DNA and the bacterial cell membrane, facilitating DNA uptake upon heat shock.

Why other options are incorrect:

  • Sodium chloride: Monovalent cations like \( \text{Na}^+ \) do not effectively facilitate membrane permeability for plasmid entry.


  • Potassium chloride: Does not provide the necessary divalent charge shielding required for efficient bacterial competence.


  • Cesium chloride: Typically utilized in density gradient ultracentrifugation for nucleic acid purification, not competence induction.

Quality & Fidelity Assurance: Every question on BeambePrep is rigorously curated against the official PMDC syllabus with zero filler, zero out-of-syllabus content, and zero typos. When an authentic past paper originally contained a historical mistake or ambiguity from the examining board (such as UHS or NUMS), BeambePrep faithfully reflects the original paper while detailing the nuance and scientific consensus in the autopsy above.

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