THE BASIS FOR TRANSGENIC ORGANISMS

TRANSFORMATION The incorporation of a piece of naked DNA (not attached to cells) from one organism into the DNA of another organism. The result is a transgenic organism.

Why does genetic engineering work? What do you know about the genetic code? The sequence of nucleotide bases on a DNA molecule makes up the genetic code. Each triplet of three bases codes for a particular amino acid. Using this code, a cell can produce any one of the many proteins that it requires. One of the many remarkable features of the genetic code is that it is universal; the three bases code for the same amino acid whether it is in a bacterial cell or a cell from another organism.

So what opportunity does this create? A gene taken from one organism should then be able to produce exactly the same product if it is introduced into another organism. This is the basis of genetic engineering, the production of new characteristics by the insertion of a gene from one organism. Genetic engineering has paved the way for many biotechnology products in medicine, agriculture, environmental products and industrial applications.

Copyright Pearson Prentice Hall Transgenic Organisms – Transgenic Microorganisms Transgenic bacteria produce important substances useful for health and industry. Transgenic bacteria have been used to produce: – insulin – growth hormone – clotting factor

The basic principles A number of different techniques are used: What stages are needed? 1. The isolation of the desired gene required to produce the product, (How can we do this?) 2.Insertion of this foreign gene into the DNA of a host cell by using a suitable DNA carrier called a vector, (What is meant by suitable?) 3.Checking to find the host cells which contain the new gene, (How do we know? Think antibiotic resistance) 4.Multiplying or cloning the organism containing the new gene to produce large numbers of genetically identical cells or organisms for commercial

Copyright Pearson Prentice Hall Transgenic Organisms – Transgenic Plants Transgenic plants are now an important part of our food supply. Many of these plants contain a gene that produces a natural insecticide, so plants don’t have to be sprayed with pesticides.

Copyright Pearson Prentice Hall – Transgenic Animals Transgenic animals have been used to study genes and to improve the food supply. Mice have been produced with human genes that make their immune systems act similarly to those of humans. This allows scientists to study the effects of diseases on the human immune system. Transgenic animals are also becoming useful commercially. On February 6, 2009 the US FDA approved the first human biological drug produced from such an animal, a goat. The drug, Atryn, is an anticoagulant which reduces the probability of blood clots during surgery or childbirth. It is extracted from the goat's milk

Restriction endonucleases or restriction enzymes: A little history In the early 1970s, researchers discovered restriction endonucleases in bacterial cells. These enzymes are now known to be part of the natural defense system of bacteria against bacterial viruses. They cut the virus DNA into small fragments and stop the infection process. There are many different types of restriction enzymes, each one cutting the DNA at a specific nucleotide sequence. Some cut the DNA straight across. Others produce a staggered cut; a sequence of unpaired bases called “sticky ends”. These are very important as they can join with complementary sticky ends on other pieces of DNA.

Production of sticky ends and recombinant DNA

Plasmids as Vectors Transformation needs Antibiotic resistance gene Gene of interest Replication site incorporated in the plasmid for successful transfer of a trait

Bacteriophage (virus) as vectors Sticks to the surface of the cell and injects genetic information into bacteria The viral genes make more bacteriophages in the bacteria using the bacterial DNA This leads to destruction of the bacterium When the bacteria split open, viruses burst out

YEAST ARE ANOTHER GOOD VECTOR

Examples

Glow mice: the jellyfish gene which causes them to glow is inserted into the mouse’s sperm before that sperm fertilizes the egg

Chimeric Mouse