You Are Performing a Bacterial Transformation Where You Are Trying

Essay

You are performing a bacterial transformation where you are trying to transfer DNA that contains the gene for resistance to the antibiotic ampicillin into the bacterium E.coli.Ampicillin normally kills E.coli,but if you are successful in your transfer of the DNA,the E.coli will now be unaffected by ampicillin.E.coli grows best on Luria Broth agar plates.Giving a cold period and then a brief heat shock and a cold period has been shown to help bacteria cells take up pieces of DNA.
You take some cultures of E.coli,add cold calcium chloride,keep these on ice for 15 minutes,heat shock them for 90 seconds,then chill them on ice for 1 minute before putting them onto Luria Broth agar plates with ampicillin and Luria Broth plates without ampicillin.These bacteria should be killed by the plates with ampicillin.
You take some other cultures of E.coli,add cold calcium chloride,then add the new DNA,then keep these on ice for 15 minutes,heat shock them for 90 seconds,then chill them on ice for 1 minute before putting them onto Luria Broth agar plates that contain ampicillin and Luria Broth agar plates without ampicillin.If you successfully transferred the DNA,these bacteria should grow on the plates with ampicillin and the ones without ampicillin.
In this experiment,why were the colonies without the added DNA and the colonies with the added DNA treated the same way (15 minutes cold,then heat shock,then cold)?