Behold, my trusty bag of Legos … well they’re not actually Legos because I couldn’t find a bag of plain old Legos. All of the Legos nowadays are sold in kits with wheels and roofs and other things I don’t want. So I bought a big bag of plastic bricks that LOOK like Legos. Here they are:
I bought them because my students have such a hard time with the basics of cell chemistry for biology. The main idea I am trying to teach is that food consists of complex organic molecules (proteins, polysaccharides, nucleic acids, and fats) that are broken down into amino acids, monosaccharides, nucleotides, glycerol, and fatty acids via hydrolysis reactions in digestion. These small molecules enter the bloodstream and are distributed to cells, which use them to build their own large molecules or use them in respiration. It’s easy once you know how it works, but it’s pretty hard to learn it for the first time.
So I started using my Legos … err, plastic bricks … in Action Center, to help students use their hands to work with the ideas. Here is my strategy, in pictures.
1 — Food represents a mixture of organic molecules. Imagine that the assembly of blocks pictured below is a bite of a bacon, lettuce, and tomato sandwich. It contains proteins, polysaccharides, nucleic acids, and fats — the different shapes and colors of the bricks represent these different molecules.
2 — In the intestines, digestion (hydrolysis) breaks the food into smaller molecules.
3 — These small molecules enter the bloodstream, and cells take them up. Here are a bunch of monosaccharides taken up by a cell.
4 — The cell uses the monosaccharides in respiration (you’d have to smash a brick into bits to illustrate this idea). Or the cell may use them to build polysaccharides, like glycogen, by dehydration synthesis. Below is a “glycogen molecule.”
5 — Cells also absorb amino acids from the bloodstream. Here are a bunch of amino acids taken up by a cell. Notice that the monosaccharides in photo #4 all looked the same, because they were all glucose. The amino acids all look different, thanks to their different R groups.
6 — The cell assembles the amino acids into proteins, again by dehydration synthesis.
7 — Now if another animal eats this organism, what will happen to the proteins, polysaccharides, and other large organic molecule the cell has produced? Why, they’ll be dismantled again, in hydrolysis.
In my experience, building and taking apart these molecules has been really helpful to students in learning the connections between digestion, hydrolysis, dehydration synthesis, and respiration.
Try it yourself! And if you have other ideas for teaching cell chemistry that have worked for you, please share them here.