Genetic engineering

Introduction

Previous chapters discussed the genetic code. All living things carry their genetic information in their chromosomes. During protein synthesis, the sequence of amino acids is specified by DNA codons that are sometimes called genetic instructions. Changes to these genetic instructions lead to changes in protein structure. Changes in protein structure lead to changes of an organism's characteristics. Sometimes these changes happen naturally and sometimes they are induced. This chapter looks at the science that deals with genetic modification of organisms, genetic engineering.

What is genetic engineering?

The science of changing an organism's genetic information is called genetic engineering. The first big success for genetic engineering (GE) was the production of insulin, a hormone produced by the pancreas, by genetically-modified bacteria. Today, genetic engineering techniques are used in many areas. For example in medicine, it is sometimes possible to find out how some diseases and abnormalities occur by reading DNA sequences. It might be possible to fight some diseases by changing the DNA codons that cause them. In pharmaceuticals, powerful antibiotics can be created by altering the genetic code of organisms which produce antibiotics. Altering the genetic code of plants and animals in agricultural practices leads to improved food products.

Manipulation of genes

By varying the sequence of DNA codons, different types of protein can be synthesised leading to an enormous variety of biological life. Genetic engineers take out one or several genes of the DNA from one organism and insert this into the DNA of another organism. This set of 'cut out' genes is called the insertion package. The organism that receives the insertion package is called the recipient organism. See image 1.

Insertion packages carriers

1. Bacteria

Bacteria make good 'vehicles' for insertion packages. Before the gene is inserted, it is hooked on the bacterial DNA. Then the recipient cells are infected by this bacterium. The bacterial DNA carrying the engineered gene is inserted into the DNA of the recipient.

2. Viruses

Viruses are made of a DNA molecule encapsulated within a protein shell. A virus can replicate itself only within the cells of a living host. When the recipient cell is infected with the carrier virus, its DNA enters the cell's nucleus and starts replicating.

3. Mechanical methods

Genes can also be inserted mechanically. In this case the insertion package is attached to a very small golden bead that is later 'fired' into the nucleus of the recipient. Sometimes a solution with genes is injected into the cell. This method is called microinjection.

Markers

It is almost impossible to put the insertion package into a specified chromosome locus. Even if the gene package is successfully inserted, it may attach to a region of non-active DNA. So it will be very difficult to determine if the insertion has been successful. Marker genes are used in one set with the engineered gene to monitor the insertion. A gene with a known location on a chromosome is called a marker.

Promoters

A promoter gene is also often added to the insertion package. The promoter is a segment of DNA that acts as a controlling element in the expression of a gene. Promoters are natural parts of chromosomes. Their function is to enhance the activity of a certain gene. Normally, promoters are controlled by regulator genes that turn them on and off. But in genetic engineering these regulators are not present as the promoter comes from another organism. This means that in most cases the promoter would 'over stimulate' the newly-inserted gene, disturbing the cellular balance.

Dolly the sheep

Dolly the sheep was the first mammal successfully cloned from an adult cell. To clone an organism means to duplicate it without the help of sexual reproduction. See image 2.

Genetically engineered (GE) food

GE food is also known as bioengineered or transgenic food. It is the type of food that has been produced using the genetic engineering process. The genetic code is altered to modify the size, taste and weather resistance of some fruits and vegetables. Animals used for food are also being genetically modified to enhance the amount and quality of the meat they produce. See image 3.

Genetically engineered food has not been around for long. It is hard to predict the outcome of using GE food for a long period of time. Many scientists are concerned that engineered organisms might harm people's health and the environment. For example, engineered crops might contaminate the food supply with drugs, kill beneficial insects and jeopardise valuable natural resources. Also, the genes of the insertion package may lead to the creation of new viruses and bacteria.