46. Plasmid DNA (0.5 μg) containing an ampicillin resistance marker
was added to 200 μL of competent cells.
The transformed competent cells were diluted 10,000 times,
out of which 50 μL was plated on agar plates containing ampicillin.
A total of 35 colonies were obtained.
The transformation efficiency is __________ × 106 cfu·μg−1.
Transformation Efficiency Calculation (cfu·μg−1)
Transformation efficiency measures how effectively competent cells take up plasmid DNA.
It is expressed as colony-forming units per microgram of DNA (cfu·μg−1).
In this case, 35 colonies were obtained after transforming cells with
0.5 μg plasmid DNA, resulting in a transformation efficiency of
7 × 106 cfu·μg−1.
Standard Formula
Step-by-Step Calculation
Substituting values:
This value lies well within the expected range for chemically competent cells,
indicating a successful transformation.
Common Pitfalls Explained
- Ignoring dilution factor: Leads to underestimation by 10,000×.
- Assuming full volume plated: Overestimates efficiency.
- Incorrect unit scaling: Forgetting that results are often expressed in ×106.
Why Transformation Efficiency Matters
High transformation efficiency (106–108 cfu·μg−1)
is essential for cloning, gene expression, and genome engineering experiments.
Lower values may indicate poor cell competency, suboptimal heat shock,
or degraded plasmid DNA.
Applications in Biotechnology
- Cloning and plasmid propagation
- Recombinant protein expression
- CRISPR and strain engineering
- Frequently tested in GATE and university exams
