Strawberry DNA Extraction

Background
In this lab, our group extracted DNA from strawberries. We accomplished this by breaking open the strawberry nuclei using various techniques and isolating the DNA in a test tube. We then forced the DNA to precipitate.

Materials
strawberries (1)
salt
detergent
gauze (cut into squares)
funnel
ethanol (ice cold)
ziploc bag (1)
pipette (1)
clear stirring rod (1)
paper cup (1)
test tubes (2)

Procedure
1. First, we made the DNA extraction buffer. To do this, we first measured out 45 mL of water in a clear test tube. Then, we measured out 0.75 g of salt by first determining the weight of the paper cup and pouring out salt as needed until the scale read the paper cup's weight plus 0.75 g. We then retrieved 5 mL of detergent in another test tube. Finally, we poured the salt and detergent into the test tube with water to make a 50 mL extraction buffer.

Measuring the salt

Making the buffer

2. After making the buffer, we washed the strawberry and removed its leaves. We then placed it into a ziploc bag, added 10 mL of the extraction buffer, and tightly sealed the bag and all, making sure that no air bubbles were present.


3. We then crushed the strawberries thoroughly for about 1 minute.

Explanation of Steps 1-3

The solution buffer consisted of water, salt, and detergent. The purpose of each was

water: to act as a solvent to the salt, detergent, and extraneous material in the strawberry cells

detergent: to split the fatty acids in the nuclear membranes of the strawberry cells, such that we could breach the nucleus and expose all the lovely DNA. We used detergent because it is nonpolar and could serve this purpose well. 

salt: because salt is an ionic compound (NaCl), it is polar. Because DNA is also polar because of the hydrogen bonding between the nucleotides, salt attracted clumps of DNA together and kept them together.

4. After we crushed the strawberries, we took some gauze and lined the funnel with it, and placed the funnel in another test tube. 

5. Then, we poured the contents of the ziploc bag (the crushed strawberries) through the funnel lined with gauze in order to filter the DNA out from extraneous material. 

6. After discarding the pulp and the gauze, we added an amount of ice cold ethanol equal to the amount of solution left. After swirling it with the stirring rod, the DNA then precipitated and we could observe it on the top of the test tube. (pics below)

The Results!!!!

Cool! Strawberry DNA!

7. Finally, after observing the DNA for a while, we collected it on the rod and observed it.

Strawberry DNA on the rod

Explanation of Steps 4-7

The gauze was employed in order to separate the strawberry DNA from the extraneous material in the strawberry cells. By filtering the contents of the ziploc bag through the funnel lined with gauze, we ensured that all the pulp would not interfere with the DNA that went into the test tube. Furthermore, we used the ethanol to precipitate the DNA. This is because ethanol is more polar than DNA. Because of the difference in solubility between the ethanol and the strawberry solution, the DNA was forced to precipitate. We specifically used cold ethanol so that the enzymes that break down DNA would not work as fast.

Alternative Method(s)

Virtually any alternative method that involves breaking the nuclei of the strawberry open and extracting the DNA using a precipitation reaction can be used. For example, instead of crushing the strawberries, blending might be a better option because it breaks the strawberry down more efficiently, perhaps too efficiently. Nonpolar molecules can be used to breach the fatty acids in the nuclear membranes and open the nucleus. In addition, any polar molecule such as different ions can be used to clump the DNA together, because of the hydrogen bonding. 

Conclusion and Discussion of Genes

From this chapter, we have learned that a gene in reality is just a sequence of instructions for making certain polypeptides. In this context, DNA is really just a molecule that contains the instructions for synthesizing polypeptides. In context of this activity, the DNA that we extracted contains all these instructions to synthesize the proteins necessary for the strawberry. The genes in the DNA that we extracted contains information for synthesizing proteins that carry out functions in the strawberry such as giving it its red tint, forming seeds, and ripening the strawberry.