4.11 - Genetic engineering methods

4.11 — Higher: Cutting, joining and carrying DNA

Higher tier: 4.11. Genetic engineering deliberately changes an organism’s genome to introduce a desirable characteristic. This lesson explains a method for carrying a selected gene into a cell; the gene must then be expressed for its protein to be produced.

The process can be modelled using a bacterial plasmid, a small circular DNA molecule, as the vector. A vector is a carrier that transfers a selected DNA segment into a recipient cell. The named components in 4.11 have different jobs, and their order matters.

1. Cut out the desired gene. A suitable restriction enzyme cuts the donor DNA at particular base sequences, producing a DNA fragment containing the desired gene.
2. Cut open the vector. The same restriction enzyme cuts the plasmid. In this model, it makes staggered cuts that leave short, exposed single-stranded sections called sticky ends.
3. Pair and join the DNA. The sticky ends on the gene fragment and cut plasmid have complementary base sequences, so they pair. DNA ligase then seals the breaks in the DNA, joining the gene fragment into the plasmid. The result is a recombinant plasmid, containing DNA from different sources.
4. Carry the gene into a cell. The recombinant plasmid acts as a vector and transfers the gene into a recipient cell. The intended result is that the recipient cell's genetic material is modified so the introduced gene can be expressed and its protein made.