In the new AQA GCSE Biology, DNA structure is much more detailed and protein synthesis is now included. In recent years protein synthesis has moved from A2, to AS and is now in the GCSE course. It’s a tricky but exciting topic to teach. Here’s how I did it:
We’d had an introductory lesson learning the basics of DNA and using the Biorad “Genes in a Bottle” kit to make DNA necklaces – the students knew that DNA acted as a code for “how to build everything in a living thing” and that it existed on strands called chromosomes.
In the second lesson we build a giant polynucleotide using a template that I found online (huge apologies – I can’t remember the source but it’s perfect and thanks so much. I edited the document I found a little bit to make it more economical to photocopy).
I’d tried to save time by making sure each student had 10 sugars and 10 phosphates in a stapled pack. I had four pots with the bases ready for collection once they’d made their backbones. The first students to finish were responsible for assembling the short 5 base pair sections into a long chain.
In the next lesson we started the slightly harder content: how the DNA strand codes for protein. I asked students to imagine our classroom was a pancreas cell (which was a good opportunity to revise basic animal cell structure). We talked about protein from a steak being digested elsewhere in the school. I opened the classroom door to represent a protein channel allowing amino acids into the cell and asked them to imagine the amino acids floating around in the cytoplasm of the cell. I talked about there being 20 different amino acids that are the building blocks of all of the proteins in the body; students could name many uses of proteins in the body.
I told students I’d explain how the proteins were built using an analogy and that we’d then use the correct words. Our analogy was reading a recipe from an old, special recipe book
Jack quickly got the idea that we’d want to take a photocopy of the right recipe and take the photocopy to the kitchen. I asked him who would take control of the recipe, expecting an answer of a chef, but I got the reply “Mrs Stewart!” (one of our Food and Nutrition teachers – well, it works!). I acted out Mrs Stewart reading the recipe calling for one ingredient at a time.
Then we moved to the back of the room where our DNA model was hanging from the ceiling. Prior to the lesson I’d scattered yellow, orange, green and blue hole-punched cards with AA (amino acid) written on around the room. I then told the class we needed to translate the analogy to real biological terms. They quickly got the idea that Mrs Stewart was the ribosomes (Jack was assigned the role of ribosome). I showed them how the DNA was “photocopied” into mRNA by having some pre-made nucleotides ready at the back and a glue stick. I’d crossed out the ‘deoxy’ from the ‘deoxyribose’ label and crossed out thymine and changed it to uracil. I told them not to worry about these changes, but that RNA was really similar in structure to DNA, but I’d made these changes to I could use the materials with the sixth form. We built up the mRNA strand which gave them the chance to practice shouting out the complementary base to the DNA strand. I then showed the mRNA floating out the nucleus and attaching to the ribosome (I draped it over Jack’s head). In the previous lesson we’d talked about the triplet code so they knew Jack would read 3 bases at a time. Four students were assigned the role of tRNA and wore card labels. I did the ‘reading’ for Jack to start with, e.g. “GGC – that codes for a green amino acid”, at which point my green-seeking tRNA student would go and hunt down a green amino acids in the lab and bring it to Jack. Then I would say “AGA – that codes for a red amino acid” and so on. Jack’s job was to use treasury tags to bond together the amino acids and form a long chain.
Once we’d made the long chain we discussed folding of proteins (e.g. the orange ones like to form other bonds – and we looped the treasury tags back). It was also a good chance to start talking about mutations and their effects.
During the lesson, more able students asked about why all proteins aren’t made all of the time which led to an interesting one-on-one chat about transcriptional factors!
Question sheet for DNA structure (based on AQA A-level questions)
Protein synthesis questions: