Introduction

Encyclopædia Britannica, Inc.

Almost every living jail cell holds a vast storehouse of information encoded in genes, segments of deoxyribonucleic acrid (Deoxyribonucleic acid) that control how the cell replicates and functions and control the expression of inherited traits. The artificial manipulation of one or more genes in order to modify an organism is chosen genetic engineering.

The term genetic engineering initially encompassed all of the methods used for modifying organisms through heredity and reproduction. These included selective convenance, or artificial selection, as well equally a wide range of biomedical techniques such as artificial insemination, in vitro fertilization, and cistron manipulation. Today, however, the term is used to refer to the latter technique, specifically the field of recombinant Deoxyribonucleic acid technology. In this procedure DNA molecules from two or more than sources are combined and then inserted into a host organism, such as a bacterium. Within the host jail cell the inserted, or foreign, Dna replicates and functions forth with the host Dna.

Recombinant Deoxyribonucleic acid engineering science has produced many new genetic combinations that accept had cracking affect on science, medicine, agriculture, and manufacture. Despite the tremendous advances afforded to order through this engineering science, withal, the practice is not without controversy. Special concern has been focused on the use of microorganisms in recombinant engineering science, with the worry that some genetic changes could introduce unfavorable and possibly unsafe traits, such as antibiotic resistance or toxin production, into microbes that were previously costless of these.

History of Genetic Engineering

Genetic engineering had its origins during the late 1960s in experiments with bacteria, viruses, and plasmids, modest, free-floating rings of Dna found in bacteria. A central discovery was made by Swiss microbiologist Werner Arber, who in 1968 discovered restriction enzymes. These are naturally occurring enzymes that cut DNA into fragments during replication. A year later American biologist Hamilton O. Smith revealed that one type of restriction enzyme cut Deoxyribonucleic acid at very specific points in the molecule. This enzyme was named type II restriction enzyme to distinguish it from type I and type III enzymes, which cutting Dna in a different fashion. In the early 1970s American biologist Daniel Nathans demonstrated that type II enzymes could be used to manipulate genes for enquiry. For their efforts Smith, Nathans, and Arber were awarded the 1978 Nobel prize for physiology or medicine.

The truthful fathers of genetic engineering were American biochemists Stanley Cohen and Herbert Boyer, who were the first scientists to use brake enzymes to produce a genetically modified organism. In 1973 they used blazon II enzymes to cut Deoxyribonucleic acid into fragments, recombine the fragments in vitro, and and so insert the foreign genes into a common laboratory strain of bacteria. The foreign genes replicated along with the bacteria'due south genome; furthermore, the modified bacteria produced the proteins specified by the strange Dna. The new historic period of biotechnology had begun.

How Genetic Engineering Works

Encyclopædia Britannica, Inc.

The activity of restriction enzymes—also chosen restriction endonucleases—is the crux of genetic engineering. These enzymes are found only in bacteria, where they protect the host genome against invading foreign DNA, such every bit a virus. Each restriction enzyme recognizes a brusk, specific sequence of nucleotide bases in the Deoxyribonucleic acid molecule. These regions, called recognition sequences, are randomly distributed throughout the DNA molecule. Dissimilar bacterial species make restriction enzymes that recognize dissimilar nucleotide sequences. By convention, restriction enzymes are named for the genus, species, and strain designations of the bacteria that produce them and for the order in which they were kickoff identified. For example, the enzyme EcoRI was the first restriction enzyme isolated from the Escherichia coli (E. coli) strain RY13.

Recognition and Cleavage

Of the three types of restriction enzymes, blazon Two is the most useful in genetic engineering. Types I and Iii restriction enzymes cleave Deoxyribonucleic acid randomly, often at some distance from the recognition sequence. By dissimilarity, type II restriction enzymes cut DNA at specific sites within the recognition sequence. Each time a particular restriction enzyme is used, the DNA is cut at precisely the same places in the molecule. Today more than 3,600 type Ii restriction enzymes are known, forming a molecular tool kit that allows scientists to cut chromosomes into various desired lengths, depending on how many different restriction enzymes are mixed with the chromosome under investigation.

Blunt and Sticky Ends

Encyclopædia Britannica, Inc.

At the cleavage site, dissimilar restriction enzymes cut Deoxyribonucleic acid in ane of two ways. Some enzymes brand incisions in each strand at a point immediately reverse the another, producing "edgeless end" Deoxyribonucleic acid fragments. Nigh enzymes cut the ii strands at a point not direct opposite each other, producing an overhang in each strand. These are called "sticky ends" because they readily pair with complementary bases on another fragment.

Recombinant DNA Technology

Encyclopædia Britannica, Inc.

Genetic engineers use restriction enzymes to remove a gene from a donor organism's chromosome and insert information technology into a vector, a molecule of DNA that volition function as a carrier. Plasmids are the virtually common vectors used in genetic engineering. These are round Dna molecules found in some bacteria; they are extrachromosomal molecules, meaning that they replicate independently of the bacterial chromosome. The first stride in the process involves mixing the donor organism's Dna with a set of restriction enzymes that will isolate the gene of interest by cut it from its chromosome. In a split step, a plasmid is cut with the aforementioned restriction enzymes. The donor cistron Deoxyribonucleic acid is so spliced into the plasmid, producing a recombinant Dna (rDNA) molecule that will function as a vector, which is introduced into bacterial cells. Inside the host cells, the plasmids replicate when the leaner replicate. Considering this produces many copies of the recombinant Dna molecule, recombinant Dna engineering is often chosen gene cloning. In addition, when the bacteria's DNA initiates protein synthesis, the protein coded for by the inserted gene is produced.

Genetic Applied science in Medicine

Medicine was the first area to benefit from genetic engineering. Using recombinant Deoxyribonucleic acid technology, scientists tin produce big quantities of many medically useful substances, including hormones, immune-arrangement proteins, and proteins involved in claret clotting and blood-cell production. Before the appearance of genetic applied science, many therapeutic peptides such equally insulin were harvested from human cadavers and the pancreases of donor animals such as pigs or horses. Using strange (nonhuman) proteins posed serious risks: in some patients the introduction of foreign proteins elicited serious allergic or allowed reactions. Furthermore, there was a great risk of inadvertently transmitting viruses from the donor tissue to the patient. Past using homo DNA to produce proteins for medical utilise, such risks were greatly decreased, if not eliminated.

Insulin and other Therapeutic Proteins

The commencement genetically engineered product canonical for homo utilise was human being insulin. Insertion of the human insulin gene into bacteria was accomplished by the pioneer genetic engineering company Genentech. Following extensive testing and authorities approval, large-calibration production of genetically engineered homo insulin was carried out, with recombinant human insulin start marketed to diabetics in 1982. Today, genetically engineered man growth hormone, parathyroid hormone, and similar proteins have provided a new standard of care to individuals suffering from endocrine diseases.

The interferons also were amongst the first recombinant proteins produced for therapeutics. Interferons belong to a class of immune-arrangement proteins called cytokines and are used to treat viral infections and some cancers, notably the virulent course of Kaposi'due south sarcoma mutual in patients with AIDS. Before the advent of genetic applied science techniques, it took laborious processing of thousands of units of human blood to obtain enough interferon, of somewhat impure quality, to treat a few patients. Genetic engineering enables the toll-effective production of vast quanties of very pure recombinant interferons.

Recombinant technology is used to produce a wide range of therapeutic substances. These include cytokines, interleukins, and monoclonal antibodies, all of which are used to fight certain viruses and cancers. Disquisitional blood factors are at present mass-produced through recombinant engineering; these include clotting proteins such as factor VIII, used to care for bleeding disorders such as hemophilia; erythropoietin, which stimulates ruddy claret jail cell production and is needed to combat anemia; and tissue plasminogen activator, a protein that helps deliquesce the claret clots that block arteries during a heart attack or sure types of stroke.

Vaccines

Genetic engineering has also provided a means to produce safer vaccines. The first step is to identify the cistron in a disease-causing virus that stimulates protective immunity. That factor is isolated and inserted into a vector molecule such every bit a harmless virus. The recombinant virus is used equally a vaccine, producing immunity without exposing people to the affliction-causing virus.

Diagnostics

Recombinant Dna applied science is also used in the prenatal diagnosis of inherited diseases. Restriction enzymes are used to cut the Dna of parents who may deport a gene for a congenital disorder. These fragments are compared with Dna from the fetus. In many situations the disease status of the fetus tin can be determined. This technique is used to detect a broad range of genetic disorders, including thalassemias, Huntington's disease, cystic fibrosis, and Duchenne muscular dystrophy.

Gene Therapy

In gene therapy, scientists use vector molecules to insert a functional cistron into the cells of individuals suffering from a disorder acquired by a defective cistron. Vector molecules containing a functional gene are inserted into a civilisation of the patient's own cells, which and so evangelize the inserted genes to the targeted diseased organs or tissues. The virtually ordinarily used vectors in gene therapy are viruses. In the target (human host) jail cell, the virus "unloads" the inserted cistron, which then begins functioning, restoring the cell to a healthy state. Another method is to take a prison cell from the patient, use recombinant engineering to remove the nonfunctional gene and replace it with a functional i, let the prison cell to replicate, so infuse the engineered cells directly into the patient. For instance, to treat the life-threatening deficiency of the immune system protein adenosine deaminase (ADA), scientists infuse cells from the patient'due south own claret into which researchers have inserted copies of the gene that directs production of ADA. Although there are still a number of challenges to overcome in developing gene therapy, it remains a research expanse of great promise.

Genetic Engineering in Industry

Genetic technology has been especially valuable for producing recombinant microorganisms that have a broad variety of industrial uses. Among the near important achievements have been the production of modified bacteria that devour hydrocarbons. These microbes are used to destroy oil slicks and to clean upwards sites contaminated with toxic wastes. Genetically engineered microbes are used to produce enzymes used in laundry detergents and contact lens solutions. Recombinant microbes besides are used to make substances that can exist converted to polymers such as polyester for use in bedding and other products.

Genetic Engineering science in Agronomics

The use of recombinant DNA in agriculture has immune scientists to create crops that possess attributes that they did non have naturally and that improve crop yield or boost nutritional value. Such crops are termed genetically modified organisms (GMOs). Past manipulating plant genes, scientists accept produced tomatoes with longer shelf lives and pest-resistant potatoes. Genetic engineering has also been used to boost the nutritional value of some foods. "Gilded rice" is a variety of white rice to which the gene for beta-carotene—a precursor of vitamin A—has been added. This nutrient-dense rice was developed for populations in developing countries where rice is a staple and where vitamin-A deficiency is widely prevalent.

The practice of producing genetically modified organisms is not without controversy. Some government agencies and ecologists, equally well as numerous consumer groups, have voiced serious reservations about the safety of such organisms and the products produced using them. While many of these objections accept merit, information technology is unlikely that the employ of genetic engineering in agronomics will exist halted. Although GMOs are banned in some countries, the vast majority of the soybeans, cotton wool, and corn raised commercially in the United States are genetically modified.