Strawberry DNA Extraction Lab

Purpose

DNA from a strawberry was extracted and viewed without a light microscope.

The materials were as follows:

• zip lock plastic bag
• 1/2 strawberry
• 10 mL DNA exraction buffer
• 2″ x 2″ cheesecloth (gauze) square (a strainer will also do)
• funnel
• ice cold alcohol
• plastic transfer pipette
• test tube
• wooden splint

The DNA extraction buffer was made of dish washing detergent, salt, and water. After rinsing the strawberry and placing it into the zip lock plastic bag (it should already contain 10 mL of the DNA extraction buffer), the strawberry was mashed for one minute against the lab table.

Afterward, the strawberry solution was poured through the strainer, purifying the solution by removing solid or fibrous parts. Finally, an equal layer of alcohol was poured on top of the strawberry solution in the test tube.

Results

The central question answered here is stated below:

Describe what you observe. What do you think is the DNA?

Picture above: courtesy of Mr. Wong/from DNA extraction handout (see the bottom of this blog post)

Twirling the wooden splint through the tube revealed tiny, transparent DNA molecules swirling in the alcohol in the shape of a tornado before eventually disappearing. Most of the DNA in the above picture is concentrated in the middle. Eventually, DNA rises to the top of the alcohol, forming a thick mucus-like substance as shown in the picture below.

The yellow instrument is the stirring tool used in the experiment. Attached to it is DNA with mucus-like properties. The test tube has two distinct layers, one of alcohol where the DNA molecules can be found. The bottom layer is reddish, with the main concentration of the strawberry solution.

Final Thoughts

Everything in the procedure served a clear purpose from adding the DNA extraction buffer to the alcohol in the final step.

What purpose does the crushing/mashing serve?

At this step, DNA extraction buffer is already present in the zip lock bag. Crushing/mashing the strawberry exposes more surface area to the extraction buffer. The purpose of the extraction buffer is discussed in the next question.

What purpose does the extraction buffer serve?

Composed of soap and salt, the extraction buffer has two key roles. The soap dissolves the cell membrane due to the like dissolves like rules (non-polar covalent [dishwashing detergent soap] dissolving non-polar covalent [cell membrane]). Secondly, the salt removes the proteins bound to the DNA. It also keeps the proteins dissolved in the water, so they don’t solidify in the alcohol with the DNA.

What purpose does the gauze serve?

It purifies the strawberry mixture, separating its liquid component. This is important as the liquid component has a high surface area exposed to the surrounding medium, as opposed to solid, fibrous strawberry components in the mixture.

What purpose does the alcohol serve?

The alcohol helps the DNA clump together to become visible. It forces the DNA to form a precipitate in the test tube solution.

Acknowledgements

Thanks Mr. Wong for letting us do this awesome lab!

Attached below is a copy of the DNA extraction handout, used for this lab procedure.

DNA Extraction Handout