Question

1. The next day when you and your lab partner returned to lab and ready to perform DNA extraction. You noticed your LB tubes are cloudier than other groups’ tubes. Your lab partner convinced you that it might because you picked larger colony last time, thus having more cultures in the LB tubes than other groups. After you performed your extraction and obtained data in normal range, you decided to continue your experiment. However, as your TA come around and checked your lab notes, he tells tell you that there is already a big problem in your experiment, and mostly you will have to re-do the experiment. What happened?

Answer 1

this is because your cells are in the stationary phase where the rate of production and destruction is almost equal. during cell death, all the components of the cell come out. it also contains DNase enzyme which degrades DNA. when you perform DNA extraction you added DNase inhibitor so that you'll get the intact DNA.

now, in this case, you'll get both the DNA- intact as well as fragmented. when you run a gel of this extracted DNA it looks like a smear. form this gel you might misinterpret that your DNA extraction protocol is not good and you have not handled DNA extraction in a good manner.

but the correct reason is more growth of the culture. so you have to repeat the extraction experiment.