Recombinant DNA Simulation - How Can Bacteria Make Human Proteins?

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Student Worksheet: Recombinant DNA Simulation - How Can Bacteria Make Human Proteins? (Google Doc file)

Goal: Students will understand how restriction enzymes are used to create recombinant DNA, as used is medical technology to create insulin.


DNA recombination with plasmids involves the intentional combining of genetic material from different sources, often for specific purposes like creating recombinant DNA molecules or expressing particular genes.

Plasmids, which are small, circular DNA molecules found in bacteria, are commonly used in genetic engineering and DNA recombination experiments due to their ability to replicate independently within bacterial cells.

In this activity, students model the process of selecting and inserting a target gene into a bacteria, so that the bacteria will produce a desired protein. In this case, the insulin gene in humans is inserted into bacteria. The result is bacteria that can make insulin.

The model is done with paper, so students will be cutting and pasting the target gene from a human sequence into a bacteria plasmid. Students must choose the appropriate restriction enzyme to cut the human insulin gene and the bacterial plasmid so that the "sticky ends" will fit together, creating a new sequence.

Step-by-step explanation of DNA recombination using plasmids:

  1. Isolation of Plasmid DNA: The plasmid DNA is isolated from bacterial cells. This involves breaking open the bacterial cells and extracting the plasmids.

  2. Selection of Target Gene: A specific gene of interest, such as a gene encoding a particular protein or trait, is identified and isolated.

  3. Enzymatic Cleavage: Enzymes known as restriction enzymes are used to cut both the plasmid DNA and the target gene at specific locations. These enzymes create "sticky ends" on both the plasmid and the target gene. These sticky ends have complementary sequences that can base-pair with each other.

  4. Ligation: The cut target gene and the plasmid DNA are mixed together in a test tube. The sticky ends of the target gene and the plasmid DNA pair up due to their complementary sequences. DNA ligase are then used to join these fragments into a continuous DNA strand.

  5. Transformation: The recombinant plasmid, now containing the target gene, is introduced into bacterial cells through a process called transformation. Bacteria take up the modified plasmid either naturally (in some cases) or through artificial methods like heat shock or electroporation.

  6. Selection: Bacteria that have successfully taken up the recombinant plasmid can be selected using specific markers.

  7. Expression of the Inserted Gene: Inside the transformed bacterial cells, the inserted gene within the recombinant plasmid can be transcribed and translated, leading to the production of the desired protein or the expression of a specific trait encoded by that gene.

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