This is the gene that codes for the protein that you would like to produce. For example, if you would like to increase the sweetness of your corn, you will want to increase the production of a protein associated with higher sugar content in the corn. A scientist's knowledge of the protein(s) that a gene will produce is based on previous research within the scientific literature. For this activity, start with a 'known' gene associated with a protein or trait.
Once you have found the gene of interest (which codes for the protein you want to produce in the target organism), you will need to make many copies of it. This is done via a technique known as polymerase chain reaction (PCR). You can get into the specifics of PCR in your activity or you can just have the students create multiple copies of the gene of interest. For example, you could provide the students with strips of paper containing a DNA sequence that includes the gene influencing sweetness.To simulate PCR, you could provide several photocopies of the DNA sequence, or alternatively you could require the students to make the copies themselves.
You will need to find a bacterial plasmid that will act as your vector to introduce the gene of interest (the gene that codes for the protein you want to produce) into the target organism. A plasmid is a small bit of circular bacterial DNA. If the plasmid is cut, a foreign gene can easily be inserted and incorporated into the plasmid. Then, when the plasmid replicates, all copies will also include the introduced gene.
You can provide the students with circular paper cutouts of a DNA sequence to simulate a bacterial plasmid. That is, the DNA sequence would be written out in a circle, rather than a strip, to mimic the shape of a plasmid. Or, you could print out the bacterial DNA sequence on a strip and have each student tape his or her copy into a circle. Discuss with the students which bacterial vector you will use in your recombination and why. For example, you might choose E. coli as a vector to introduce an insulin-producing gene into a human, because E. coli is a human symbiont, and can easily reproduce within the human gut.
To cut apart the DNA (from both sources -- the bacterial source and the source of the gene of interest, which codes for the protein you want to produce in the target organism), you will need to use restriction enzymes. You will need to find restriction enzymes that will cut the DNA at a specific sequence that will match the complementary base pairs at the ends of the gene of interest. In this way, the freshly cut ends of the bacterial plasmid and the ends of the gene of interest will be able to bond easily. Allow the students to choose between possible restriction enzymes in the activity, and explain why the correct restriction enzyme will work best.
For example, you could provide several pairs of scissors, and tape a small tag on each that shows at which DNA sequence that 'restriction enzyme' would cut the DNA strip. Allow the students to choose which pair of scissors they want to use, and ensure that they cut the DNA strip at the correct sequence according to their restriction enzyme choice.
You will finally need to introduce the rDNA into the host organism in which you would like to increase the production of a certain protein. For example, if you are trying to produce sweeter corn, you will need to introduce the rDNA into a corn plant. Discuss with the students various methods for introducing the rDNA, and allow them to choose a method they think would work best. Discuss the answers.
Once the rDNA has been successfully introduced to the host, the host's cells will replicate the rDNA. The uptake and replication of the rDNA is known as transformation. Discuss this process and terminology with the students.
To simulate the transformation process on paper, allow the students to attach the gene of interest (ex. the gene influencing sweetness in corn), which has been cut off of its larger DNA sequence using the 'restriction enzymes' in the previous step, to the bacterial plasmid, which has also been cut open by a 'restriction enzyme' in the previous step. Use tape to attach the two DNA sequences together. You could then allow the students to make photocopies of the new recombinant DNA to simulate the replication process.