Genetic engineering is an umbrella term that can cover a wide range of ways of changing the genetic material in a living organism. This code contains all the information stored in a long chain chemical molecule that determines the nature of the organism. Apart from identical twins, genetic makeup is unique to each individual. Individual genes are particular sections of this chain, spaced out along it, which determine the characteristics and functions of our body. Defects of individual genes can cause a malfunction in the metabolism of the body and are the roots of many genetic diseases. In a sense, man has been using genetic engineering for thousands of years.
We weren’t changing DNA molecules directly, but we were guiding the selection of genes. For example, the domestication of plants and animals. Recombinant DNA technology is the newest form of genetic engineering, which involves the manipulation of DNA on the molecular level. This is a totally new process based on the science of molecular biology, a relatively new science only forty years old. It represents a major increase in our ability to improve life.
However, a negative aspect of genetic engineering is that it can alter the forms of life we are familiar with, potentially causing harm to our environment. It has been known for some time that genetic information can be transferred between microorganisms through the use of vectors such as plasmids (small circular rings of DNA) or phages (bacterial viruses). While this process is generally limited to simpler species of bacteria, genetic engineering allows for the introduction of any gene, overcoming this restriction.
Genetic engineering is being used to produce enzymes, but it depends on harnessing enzymes that are available in nature. In the early 1970s, Herbert Boyer and Stanley Cohen found that they could insert genes from one bacteria into another. They broke down the DNA of the donor organism into manageable fragments and placed them into a vector, which transported the DNA into recipient bacteria. The transported gene divided as the cell divided, leading to a clone of cells, each containing exact copies of the gene.
This technique is known as gene cloning, and it involves selecting recipient cells that contain the desired gene. The enzymes used to cleave the DNA pieces act in a highly specific manner. Therefore, genes can be removed and transferred from one organism to another with extraordinary precision. These manoeuvres contrast sharply with the much less predictable gene transfers that occur in nature.
By mobilizing pieces of DNA, including copies of human genes, genetic engineers are now fabricating genetically modified microbes for a wide range of applications in industry, medicine, and agriculture. The underlying idea of transferring genes between cells is quickly explained; however, the actual practice is an extremely complicated process. The scale of the problem can be gauged from the astronomical numbers involved: the DNA of even the simplest bacterium contains 4,800,000 pairs of bases, but there is only one copy of each gene in each cell.
First, restriction enzymes are used to snip the DNA into smaller pieces, each containing one or just a few genes. These enzymes cut DNA in very precise ways. They recognize particular stretches of bases, termed recognition sequences, and snip each strand of the double helix at a specific place. Whenever the recognition sequence appears in the long DNA chain, the enzyme makes a cut.
Whenever the same enzymes are used to break up a certain piece of DNA, they always produce the same set of fragments. The cuts produce pieces of double helix with short stretches of single-stranded DNA at each end, known as sticky ends. If the enzyme is allowed to act for a limited time, it may not have a chance to attack all the recognition sequences in the chain.
This will result in longer fragments. As in natural DNA replication, bases have an inherent propensity to join up with their partners, such as A with T and G with C. The same is true for sticky ends. For example, the sequence TTAA will tend to re-associate with AATT. Genetic engineers use another type.
