Thursday, April 19, 2018

Homeschool Biology: Extract and Visualize DNA from Beef Liver

The kids and I are using CK-12's 9th/10th grade Biology textbook as the spine for this year's biology curriculum--for Will, who is in the eighth grade but who is taking high school-level coursework, this will be recorded as Honors Biology on her transcript.

In addition to that textbook, we're using The Illustrated Guide to Home Biology Experiments as our lab manual, and of course we've got a plethora of other reading/viewing/listening resources and hands-on activities to enrich our study.

Extracting DNA from fruit is one of those go-to hands-on science stations that my kids have already done at oodles of programs and festivals (and in fact, just a couple of weeks after we did this lab, Syd attended a Girls in STEM conference one Saturday morning and lo and behold! One of their workshop activities was extracting DNA from strawberries!), so I wanted to make its iteration in the DNA chapter of our biology textbook more rigorous for these little DNA extraction experts.

Want roughly the same process as extracting DNA from fruit, but with a more involved and complicated procedure? Extract DNA from beef liver!

We followed the procedure from The Illustrated Guide to Home Biology Experiments for this, using beef liver from the local butcher shop. The process included a lot of excellent practice in making and staining slides (I still have not mastered the method of drawing stain underneath a slide cover using the corner of a paper towel) and using the microscope at different magnifications. The kids are still a little uncertain when they handle the microscope, mostly, I think, because they know how expensive and delicate it is, but after helping them run through this procedure, I feel like an old pro!

Look, everyone! Beef liver!

Syd, as you can tell, did not love mashing beef liver in a ceramic egg cup:

The coolest part of this procedure--though it's also tedious, I'll be honest--is determining the correct amount of sodium dodecyl sulfate to add to the strained beef and saline solution. The kids had to add a specific amount of sodium dodecyl sulfate to the strained beef and saline solution, make and stain a slide of that solution, and then observe it under the microscope, and then do it again. And again. And again. And again.

Worth it, though, when you finally hit the sweet spot and the cell membrane breaks down. Syd described it this way: "The cells all exploded!" Indeed, it was pretty cool!

When the cells have "all exploded" you can gently and carefully introduce the chilled isopropanol into the solution--
Here you see beef liver and saline solution in several states--the one on the left has isopropanol introduced.
 --and you can see with your naked eyes when the DNA has precipitated out. Remind the kids of all the experimenting that you did with liquid density!

As a final step you can extract the DNA from this, make and stain a slide, and observe it under the microscope.

I won't tell you what it looks like, but it was so cool--in fact, everything under the microscope in this procedure was so cool!--that I spent a hundred bucks of my homeschool budget on a digital camera/video camera that's made to go with our microscope. 

The next time we explode a cell, we'll have photographic evidence!

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