Wild strains of micro-organisms can be improved by mutagenesis, or recombinant DNA technology.

Exposure to UV light and other forms of radiation or mutagenic chemicals results in mutations.

Some mutations may produce an improved strain of micro-organism.

Recombinant DNA technology involves the use of recombinant plasmids and artificial chromosomes as vectors.

A vector is a DNA molecule used to carry foreign genetic information into another cell

Both plasmids and artificial chromosomes are used as vectors during recombinant DNA technology.

Artificial chromosomes are preferable to plasmids as vectors when larger fragments of foreign DNA are required to be inserted.

Restriction endonucleases cut open plasmids and specific genes out of chromosomes, leaving sticky ends.

Complementary sticky ends are produced when the same restriction endonuclease is used to cut open the plasmid and the gene from the chromosome.

The enzymes restriction endonucleases and ligase play a role in recombinant DNA technology.

Ligase seals the gene into the plasmid.

Recombinant plasmids and artificial chromosomes contain restriction sites, regulatory sequences, an origin of replication and selectable markers.

Selectable marker genes present in the vector ensure that only micro-organisms that have taken up the vector grow in the presence of the selective agent (antibiotic).

→ Selectable markers, such as antibiotic resistance genes, protect the microorganism from a selective agent (antibiotic) that would normally kill it or prevent it growing.

Restriction sites contain target sequences of DNA where specific restriction endonucleases cut.

Regulatory sequences control gene expression.

An origin of replication allows self-replication of the plasmid/artificial chromosome.

As a safety mechanism, genes are often introduced that prevent the survival of the micro-organism in an external environment.

→ Plant or animal recombinant DNA expressed in bacteria may result in polypeptides being incorrectly folded.

Recombinant yeast cells may be used, to produce active forms of the protein which are inactive in bacteria.