DNA Extraction Lab

Purpose | Hypothesis | Predictions | Onion and E. Coli | Wheat Germ  Conclusions | Additional Experiments


To attempt to extract DNA from different organisms, while at the same time learning the DNA extraction process.


We will be able to successfully extract DNA from the onion, both types of wheat germ, and the Escheria coli.  It will be toughest in the process used on the wheat germ, but we will be successful in all cases.  This extraction will be made possible by all of the substances that we use.  The use of each solution is explained in the "analysis" column.


Each step of the process will help in a certain way to extract DNA, until we are finally successful in the end.  In the wheat germ extraction, the ethanol will be able to separate the DNA, and it will float between the less dense ethanol and the denser homogenizing mixture.  In the onion extraction, the chloroform and homogenizing medium will help break down the cell membranes, and the ethanol, like in the wheat germ extraction, will cause the DNA to separate and be suspended in the interface between the two solutions.

The rest of this lab will be divided between the two procedures that we used:

Onion and E. coli DNA Extraction

Wheat Germ DNA Extraction


Overall Conclusions for both labs:

We learned a great deal from the completion of these extractions.  Besides the thrill of observing DNA, the genetic messenger of life, in its visible form, we also gained an excellent knowledge of the basic procedures and techniques for extraction of DNA and other macromolecules from cells.  We made educated hypotheses about the necessity for and probable effect of each substance and method used in the extractions (documented under "Analysis") and then observed some of the actual effects of each step.  While we were not able to observe the results of the addition of some substances (for instance, the detergent that was intended to solubilize the cellular and nuclear membranes), we did observe the success of later steps that would most likely indicate our hypotheses had been correct (for instance, when the ethanol precipitated the DNA out of the wheat germ solution, it was an indication that we must have been correct in our detergent hypothesis, or the plasma membranes would have remained, making it impossible for the DNA to reach solution).  Above all, we gained invaluable experience with the essential heart of DNA technology: the extraction of the nucleic acids from cells.  Without this relatively basic procedure, the progress our society has made from Watson and Crick's observation of DNA base pairing to modern recombinant DNA and biotechnology techniques would have been unthinkable.

 The main analysis of the results of these investigations are documented in the tables above, and probable explanations for our relative failure in Quinoa and E. coli extractions are located under "Error Analysis" below.  Beyond these analyses of the processes we undertook, the purpose of this lab was mainly to gain practical experience with the processes and to apply skills of critical thinking in attempting to determine the purpose of each step in the procedure.

 Notwithstanding the shortcomings of the lab (documented under "Error Analysis"), I believe it was a highly valuable exposure to invaluable techniques of DNA technology.

Additional Experiments:

 Now that we have completed four basic DNA extractions, I would be interested in expanding our horizons significantly.  First, I would like to know what it was that caused our bacterial DNA extraction to fail (analysis of this phenomenon and of the results of other extractions are documented under "Error Analysis").  It would be interesting to repeat this procedure with the same or different species of bacterial cells to compare results.  Furthermore, it would be wonderful to find well-documented and proven methods for extraction of DNA from a wide variety of plant, animal, fungal, and bacterial cells.  I have already found a procedure for the extraction of DNA from human cheek cells.  Eventually, I believe pair of lab partners in the class could be assigned a single type of cell to extract DNA from.  This would greatly minimize confusion about the varying procedures for extractions, and would allow a multitude of organism DNA to be examined and compared.  This type of experiment could also be used in conjunction with genetic studies of Brassica rapa and other plants: once reliable procedures were established, DNA from parental and filial plants could be extracted, cut with restriction enzymes, and processed by gel electrophoresis to observe similarities and differences in genome.  The same basic procedure could be used to analyze DNA from the cheek cells of students in the class and their parents.  This type of experiment would provide a fascinating hands-on look at the nature of DNA technology and its applications in the modern world.



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