MS7- genetic control of metabolism

• Scientists may wish to change the DNA of wild strains of micro-organisms so that they produce useful substances
• wild strains of micro-organisms can be improved by mutagenesis or recombinant DNA technology
• exposure to mutagenic agents may produce an improved strain of micro-organisms
• The process of changing a micro-organism’s genetic material using mutagenic agents is called mutagenesis
• There are two main types of mutagenic agents:

  • radiation - eg UV light, X-rays and gamma rays;
  • chemical - eg mustard gas and lead oxide.
• Scientists can use advances in recombinant DNA technology to manipulate DNA within the laboratory and improve micro-organisms.
• A plant or animal gene is transferred into a micro-organism that can then make the plant / animal protein.
• During recombinant DNA technology a fragment of DNA can be cut out and inserted into a vector.
• A vector is a DNA molecule used to carry foreign genetic information into another cell.
• Recombinant plasmids and artificial chromosomes are used as vectors in recombinant DNA technology.
• Artificial chromosomes are preferable to plasmids as vectors when larger fragments of foreign DNA are required to be inserted.
• Enzymes play an important role in recombinant DNA technology.
• Restriction endonucleases are a group of enzymes that can recognise and cut specific sequences of DNA.
• Restriction endonucleases cut open plasmids and cut specific genes out of chromosomes.
• These fragments of DNA have unpaired nucleotides at the end – sticky ends
• Complementary ‘sticky ends’, with complementary base pairings, are produced when the same restriction endonuclease is used to cut open the plasmid and the gene from the chromosome.
• Ligase is an enzyme that is able to join the complementary sticky ends of two different fragments of DNA together.
• Ligase seals the gene into the plasmid.
• Recombinant plasmids and artificial chromosomes contain:

  • restriction sites;
  • regulatory sequences;
  • an origin of replication;
  • selectable markers.
• Recombinant plasmids and artificial chromosomes contain restriction sites, these contain target sequences of DNA where a specific restriction endonuclease will cut.
• Regulatory sequences can also be found on recombinant plasmids and artificial chromosomes which control gene expression.
• the origin of replication allows the plasmid or artificial chromosome to self-replicate.
• It ensures that the modified plasmid is copied and passed on to daughter cells when the transformed bacteria divides.
• Selectable markers are genes (eg antibiotic resistance gene) that protect the micro-organism from a selective agent (antibiotics) that would normally kill the micro-organism or prevent it from growing.
• Selectable marker genes present in the vector ensure that only micro-organisms that have taken up the plasmid 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.
• Recombinant yeast cells can be used as a vector to produce proteins that would normally be found in animals or plants.
• Bacterial recombinant DNA may produce animal or plant protein chains (polypeptides) that are inactive as the polypeptides are incorrectly folded.
• Recombinant yeast cells are used during DNA recombinant technology as they produce active forms of the protein.