The vector is used to insert the gene into the required cells

The idea

Once the required gene has been inserted into a vector, the vector acts as a delivery vehicle to transfer the gene into the required cells. For example, a recombinant bacterial plasmid can be taken up by bacteria, or a modified virus can inject its genetic material into a plant or animal cell. Inside the host cell, the gene is expressed so the cell manufactures the desired protein, such as human insulin. This vector-delivery step is assessed at Higher Tier only.

What earns the marks

• The vector carries the required gene into the required cells, acting as a delivery system.
• Bacterial plasmids can be taken up by bacteria, and viruses can transfer genes into plant or animal cells.
• Once inside the host cell, the inserted gene is expressed so the cell produces the desired protein.
• The host cells are often cultured or cloned so that many cells carry the gene and make enough product.

Common mistakes and how to put them right

• Saying the vector is the cell that makes the protein.

  Put it right: The vector delivers the gene, and the host cell expresses it.

• Assuming the gene works immediately outside a cell.

  Put it right: The gene must be inside a host cell for its instructions to be used.

• Confusing insertion of the gene into the vector with insertion of the vector into the cells.

  Put it right: These are separate stages; first the gene goes into the vector, then the vector inserts the gene into the cells.

Exam tips

• Use the wording 'the vector is used to insert the gene into the required cells' to match the specification statement.
• Give a named example, such as a bacterial plasmid carrying the human insulin gene into a bacterium.
• Be prepared to describe this vector delivery step on Higher Tier papers.