Introduction:

Genetic engineering encompasses techniques that have revolutionized biological research, as well as the biotechnology industry. Scientists have been able to manipulate organisms at a genetic level, to move DNA from one organism to another, and to provide the world with medications, such as human insulin and human growth hormone. The development of recombinant DNA vaccines, such as the Hepatitis B vaccine, is also an accomplishment of genetic engineering. But how is all this possible? 

Since Watson and Crick’s 1953 discovery of DNA structure, numerous tools and techniques have been developed. Gel electrophoresis is one such tool. DNA fingerprinting can identify deceased individuals from skeletal remains, perpetrators of crimes from blood or semen samples, and help determine the genetic makeup of long-dead individuals or extinct organisms. 

The use of restriction enzymes is another such tool. Restriction enzymes are produced by a number of different species of bacteria. These enzymes produce DNA fragments cut at specific base sequences, which can be linked to vectors to create recombinant DNA molecules. A vector is a segment of DNA that can carry the desired gene or gene fragment into a bacterium. If the vector and the fragment are cut with the same enzyme, they have “sticky ends” that allow them to join. The recombinant DNA can be replicated in a host to clone the inserted segment. We can retrieve the cloned DNA for study and use it to produce and purify the gene product coded for by the cloned DNA. Sounds simple, right? As you must guess by now, there are many steps and bits of evidence to consider. 

A restriction enzyme is a bacterial enzyme that stops viral reproduction by cutting the viral DNA at a certain set of sequences that are not found in the bacterial chromosome. Escherichia coli (E. coli) produces a restriction enzyme known as EcoRI that makes palindromic sequences that read the same on either strand. Restriction enzymes are named with the first three letters of the organism name (E. coli becomes Eco), the letter R indicates that this is a restriction enzyme, and a roman numeral (in this example, I) indicates this is the first restriction enzyme found in that organism. Thus, EcoRI was the first restriction enzyme found in E. coli.



Restriction enzymes, like EcoRI, create DNA molecules with single stranded tails that can form hydrogen bonds with other similarly cut DNA sequences.