unit 2 - ka7: genetic control of metabolism

• 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 of which 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 and 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.
• The role of the enzymes restriction endonucleases and ligase in recombinant DNA technology.
• 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. Ligase seals the gene into the plasmid.
• Recombinant plasmids and artificial chromosomes contain restriction sites, regulatory sequences, an origin of replication and selectable markers.
• Restriction sites contain target sequences of DNA where specific restriction endonucleases cut.
• Regulatory sequences control gene expression and origin of replication allows self-replication of the plasmid/artificial chromosome.
• Selectable markers such as antibiotic resistance genes protect the micro-organism from a selective agent (antibiotic) that would normally kill it or prevent it growing.
• 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).
• As a safety mechanism, genes are often introduced that prevent the survival of the micro-organism in an external environment.
• Use of recombinant yeast cells to produce active forms of the protein which are inactive in bacteria.
• Recombinant yeast cells may be used, as plant or animal recombinant DNA expressed in bacteria may result in polypeptides being incorrectly folded.