Enzymes cut and join the required gene

1. A restriction enzyme cuts DNA at a specific recognition sequence.
2. Use a restriction enzyme to cut the required gene from donor DNA.
3. Cut a plasmid with the same restriction enzyme so the gene and plasmid have complementary sticky ends.
4. Sticky ends are short exposed single-stranded DNA sequences that pair by complementary base pairing.
5. Mix the gene and opened plasmid so matching sticky ends join.
6. DNA ligase seals the sugar-phosphate backbone, producing a recombinant plasmid.

A vector carries the gene into cells

1. A vector is a carrier used to transfer genetic material into a cell.
2. Plasmids are small circular DNA molecules that can be removed from bacteria, modified and returned to bacterial cells.
3. Viruses can also act as vectors because they naturally insert genetic material into cells.
4. Introduce the recombinant vector into recipient cells, then use a marker to identify cells that received it.
5. Grow the selected cells by mitosis so the inserted gene is copied and its protein can be produced on a large scale.

The whole process forms a causal chain

1. The restriction site determines where DNA is cut and whether compatible sticky ends form.
2. Complementary sticky ends hold the two DNA pieces together before ligase makes the join permanent.
3. The vector protects and transports the gene, while the host cell supplies the machinery for gene expression.
4. Selection separates successfully modified cells from cells that did not take up the vector.