6. (3 pts) 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

Given:

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

(CFU is colony forming units) => (number of colonies on plate/ng of DNA plated) X 1000 ng/µg = CFU/µg of DNA

Amount of DNA used for plating = 100ng * (200/1000)

                                                      = 100ng * (1/5)

                                                      = 100/5 = 20ng

Efficiency calculation = 40 colonies / 20ng = 2 colonies/ng

               (2 colonies/ng) * (1000 ng/µg) = 2000 CFU/ug DNA

Transformation efficiency = 2000 Transformants / ug DNA

                                          = 2 x 10³ Transformants / ug DNA

Explanation:

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