Describe the main stages of genetic engineering including the use of: a…

The idea

The main stages of genetic engineering use several tools. First, the desired gene is cut out of the donor DNA using a restriction enzyme, which cuts at a specific base sequence and leaves short unpaired bases called sticky ends. A vector, such as a plasmid, is cut open with the same restriction enzyme, producing complementary sticky ends. The gene and vector sticky ends pair up by complementary base pairing. Ligase then joins the gene into the vector by forming bonds in the sugar–phosphate backbone, producing a recombinant DNA molecule. The vector carries the gene into the host cell, where the gene is expressed. Learners must match each tool to its job: restriction enzymes cut, sticky ends allow joining, ligase seals, and vectors carry the gene into the host.

What earns the marks

• Restriction enzymes cut DNA at specific sequences to isolate the desired gene.
• Restriction enzymes leave sticky ends (short unpaired bases) on the cut DNA.
• The vector, such as a plasmid, is cut with the same restriction enzyme to give complementary sticky ends.
• Sticky ends allow the gene and vector to join by complementary base pairing.
• Ligase joins the gene into the vector by forming bonds in the sugar–phosphate backbone.
• The vector carries the recombinant DNA into the host cell so the gene can be expressed.

Common mistakes and how to put them right

• Swapping the roles of restriction enzymes and ligase.

  Put it right by remembering restriction enzymes cut DNA, while ligase joins DNA.

• Thinking sticky ends are joined by ligase directly.

  Put it right by explaining that sticky ends pair by complementary base pairing, and ligase then seals the join.

• Believing any vector can take any gene without matching ends.

  Put it right by stressing that the vector is cut with the same restriction enzyme so the sticky ends are complementary.

• Forgetting the vector's role.

  Put it right by stating that the vector carries the gene into the host cell.

Exam tips

• Match each named tool to one job: restriction enzyme cuts, sticky ends pair, ligase joins, vector carries.
• When describing the order, start with cutting the gene, then cutting the vector, then joining, then transfer into the host.
• Use the phrase complementary sticky ends to explain why the gene and vector fit together.