Enzymes are used to isolate the required gene; this gene is inserted into…

The idea

Genetic engineering begins by identifying the gene coding for a desired protein, such as human insulin. Enzymes are used to cut the DNA, isolating the required gene from the donor genome. The same enzymes cut open a vector, which is typically a bacterial plasmid or a virus. This ensures complementary ends, allowing the gene and vector to join and form a recombinant molecule. The vector then acts as a vehicle to carry the gene into a host cell. These detailed enzyme-and-vector steps are assessed at Higher Tier only.

What earns the marks

• Enzymes are used to cut DNA, isolating the required gene from the donor organism's genome.
• The vector, usually a bacterial plasmid or a virus, is cut open using enzymes to prepare it for the gene.
• A vector acts as a carrier to transfer the isolated gene into a host cell.
• The isolated gene is inserted into the vector, forming a recombinant molecule before delivery.

Common mistakes and how to put them right

• Thinking any enzyme can cut DNA anywhere.

  Put it right: Specific enzymes are required to cut DNA to isolate the exact gene.

• Confusing the vector with the host cell.

  Put it right: The vector is the carrier (plasmid or virus), while the host cell is the organism that receives the gene.

• Believing the gene is inserted directly into the host without a vector.

  Put it right: The gene is first inserted into a vector, which then carries it into the cells.

Exam tips

• State clearly that enzymes are used to isolate the required gene and cut open the vector.
• When asked why a vector is used, link it to carrying the gene into the host cell rather than simply naming plasmid or virus.
• Remember that the detailed mechanism involving enzymes and vectors are assessed on Higher Tier papers.