DNA

DNA can be an abstract concept to students. It helps if the kids know what atoms and molecules are. We had already gone through that last year. I contrasted the complicated large DNA molecule with much simpler ones like water. The DNA is coiled up inside the nucleus of the cell. I also explain DNA in reference to it’s function in the cell. If you compare a cell to a castle, the DNA is an instruction book in a library (nucleus) inside the castle walls. The instruction book (DNA) describes how to make proteins which are what living organisms are made of. The body is also made of fats, minerals, sugars, small amounts of metal, and water. Some of these come from what an animal eats and others are made in the body.

Protein Synthesis

To explain the function of DNA, you must describe how proteins are made.  Proteins are made up of a string of amino acids guided by the sequence of bases in DNA. To explain this I had one child be the library (nucleus) and hold a book (DNA). In the book were sentences (genes) written out as a series of color words. The sentences have a start signal (capital letter) and an ending signal (period). I told the kids they could not remove the book from the library, but they must bring the instruction to the protein making factory (ribosomes). The kids wrote one of the sentences on a piece of paper (messenger RNA) to bring to the factory. I gave other kids (transfer RNA) one bead (amino acid) each. Then I had the kids in the factory (ribosomes) call out a color (amino acid), and a kid with that bead came up to add it on a string. This made the primary structure of the protein. I had the beads be different shapes because amino acids are different shapes. Then I explained that this string folded up into the secondary structures like beta sheets, and the final folded product is the tertiary structure. If 2 or more proteins bind together this is the quaternary structure.

DNA Extraction

It can help to actually see DNA. DNA looks like clear slime and when it is in alcohol it looks white. You can get quite a lot of DNA out of strawberries because they are octoploid. This means they have 8 full sets of chromosomes. Humans are diploid. We have two sets of chromosomes, one from our mother and one from our father. You can find a great protocol to extract DNA from strawberries with pictures here. Make sure you use strawberries because they are easy to mash up and most other fruits and vegetables are not octoploid so you would not get as much DNA from them. If you use something else you will get some DNA, but it won’t be enough to see with this experimental method. I found I got more DNA if I used very, very ripe strawberries. If you gently push up some of the strawberry solution into the rubbing alcohol layer you will get more DNA from the extraction.

DNA Gel

In the lab, you often need to run DNA on a gel. A gel is like Jell-o. The gel is put in a solution and a negative charge is run across the top and a positive charge across the bottom. This pulls the negatively charged DNA which you load into wells, through it to the bottom. Longer pieces of DNA move through slower than shorter pieces. If you imagine three children holding hands running through a dense forest compared to a group of 100 kids holding hands trying to run through a dense forest, you can imagine the group of three will get through much easier and faster. It is the same for the DNA moving through the gel.

I made an edible version of a gel with clear Jell-o for the gel and blue Jell-o that was cool, but not set to “load” into the wells with a medicine dispenser. I had some of the kids put the blue Jell-o into the wells, just like you would load DNA with loading buffer into the wells in the gel. I cut the wells out with a tic tack box with the lid taken off.