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After transformation, 40 colonies were present on the plate. What is the transformation efficiency of the...

After transformation, 40 colonies were present on the plate. What is the transformation efficiency of the competent cells if 100 ng of DNA was used for transformation of 100 ul competent cells? LB medium was added to 1 ml total volume and 200 ul were plated after 1 hour growth at 37oC.

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Answer #1

Answer:

  • Number of colonies on plate = 40
  • Amount of DNA used for transformation = 100ng
  • Volume of competent cells used = 100ul
  • Total volume = 1ml (1000ul)
  • Volume plated for growth = 200ul

The amount of cells transformed per 1 µg of DNA is called the transformation efficiency

Transformation efficiency can be calculated with the following equation (CFU is colony forming units):
(# colonies on plate/ng of DNA plated) X 1000 ng/µg = CFU/µg of DNA

  • Amount of DNA used for plating = 100ng * (200/1000) = 100/5 = 20ng
  • Efficiency calculation = 40 colonies / 20ng = (2 colonies/ng) *(1000 ng/µg)= 2000 CFU / ug DNA

Transformation efficiency = 2000 Transformants / ug DNA = 2 x 103 Transformants / ug DNA

Low transformation efficiency could be because of high amount of DNA used for transformation. Efficiency of transformation is highest in the 100 pg-1 ng range.

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