Learn about Genetic Engineering through a Few Questions and Answers

2. What is genetic engineering?

Genetic engineering is the use of genetic knowledge to artificially manipulate genes. It is one of the fields of biotechnology.

3. At the present level of advancement of biotechnology, what are the main techniques of genetic engineering?

The main genetic engineering techniques used today are: recombinant DNA technology (also called genetic engineering), in which pieces of genes from an organism are inserted into the genetic material of another organism to produce recombinant organisms; nucleus transplantation technology, popularly known as “cloning”, in which the nucleus of a cell is grafted into an enucleated egg cell of the same species to create a genetic copy of the donor (of the nucleus) individual; and DNA amplification technology, or PCR (polymerase chain reaction), which allows to produce millions of replications of the chosen fragments of a DNA molecule.

Recombinant DNA technology is used to create transgenic organisms, such as mutant insulin-producing bacteria. Nucleus transplantation technology is in its initial development but is the basis, for example, of the creation of “Dolly” the sheep. PCR has numerous practical uses, such as in medical tests to detect microorganisms present in blood and tissues, DNA fingerprinting and the obtainment of DNA samples for research.

4. What are restriction enzymes? How do these enzymes participate in recombinant DNA technology?

Restriction enzymes, or restriction endonucleases, are enzymes specialized in the cutting of DNA fragments, which each have an effect on specific sites of the DNA molecule. Restriction enzymes are used in recombinant DNA technology to obtain with pieces of DNA molecules with precision, which will later be inserted into other DNA molecules cut by the same enzymes.

• Genetic Engineering Review - Image Diversity: recombinant DNA technology restriction enzymes

5. What are DNA ligases? How do these enzymes participate in recombinant DNA technology?

DNA ligases are enzymes specialized in tying the complementary DNA chains that form the DNA double helix. These enzymes are used in recombinant DNA technology to insert pieces of DNA cut by restriction enzymes into other DNA molecules undergoing the effect of the same endonucleases.

• Genetic Engineering Review - Image Diversity: DNA ligases

6. What are plasmids?

Plasmids are circular DNA molecules present in the genetic material of some bacteria. They may contain the genes responsible for bacterial resistance to some antibiotics as well as the genes for producing proteins that cause virulence (pathogenic hostility). 

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7. How is genetic engineering used to create bacteria capable of producing human insulin?

In the production of human insulin by bacteria, the human insulin gene is incorporated into the genetic material of these microorganisms. The mutant bacteria multiply, forming lineages of insulin-producing bacteria.

Bacteria contain circular strands of DNA called plasmids, which are mini-chromosomes that act as an accessory to the primary DNA. To create mutant bacteria capable of producing insulin, a plasmid is submitted to the effect of restriction enzymes (restriction endonucleases) specialized in cutting DNA fragments. The once circular plasmid is opened by the restriction enzyme. The same enzyme is used to cut a human DNA molecule containing the insulin gene. The piece of human DNA containing the insulin gene is then bound to the plasmid at its ends through the help of DNA ligases. The recombinant plasmid containing the human insulin gene is then inserted into the bacteria.

Another human hormone already produced by recombinant bacteria is GH (somatotropin, or growth hormone).

The insertion of DNA molecules into the cells of an individual is also used in gene therapy, a promising treatment for genetic diseases. In gene therapy, cells from an organism deficient in the production of a given protein receive (by means of vectors, such as virus) pieces of DNA containing the protein gene and then begin to synthesize the protein.

8. What is cloning?

Cloning is the production of an organism genetically identical to another by means of genetic engineering.

The basis of cloning is nucleus transplantation technology. A nucleus from a cell is extracted, generally from an embryonic (undifferentiated) cell and this nucleus is inserted into a previously enucleated reproductive cell (in general an egg cell); the egg is then implanted in the organ where the embryonic development will take place. If embryonic development occurs, the new organism will have an identical genetic content to the organism organism whose cell nucleus was used in the transplantation.

• Genetic Engineering Review - Image Diversity: genetic cloning Dolly the sheep

9. What is PCR? How does PCR works?

PCR, polymerase chain reaction, is a method to synthesize many copies of specific regions of a DNA molecule known as target-regions. Its inventor, Kary Mullis, won the Nobel Prize for Chemistry in 1993.

First, the DNA to be tested is heated to cause the double helix to rupture and the polynucleotide chains to be exposed. Then, small synthetic sequences of DNA known as primers and containing nucleotide sequences similar to the sequences of the extremities of the region to be studied (for example, a region containing a known gene exclusive to a given organism) are added. The primers are paired with the original DNA at the ends of the gene to be amplified. Enzymes known as polymerases, which catalyze DNA replication, and nucleotide supply are added. The primers are then completed and the chosen region is replicated. In the presence of more primers and more nucleotides, millions of copies of that specific region are generated. (PCR is very sensitive, even when using a minimal amount of DNA).

• Genetic Engineering Review - Image Diversity: polymerase chain reaction

10. What molecular biology principle is the basis for DNA fingerprinting?

DNA fingerprinting, the method of the identification of individuals using DNA, is based on the fact that the DNA of every individual (except for identical twins and individual clones) contains nucleotide sequences exclusive to each individual.

Although normal individuals of the same species have the same genes in their chromosomes, each individual has different alleles and even in the inactive portions of the chromosomes (heterochromatin), there are differences in nucleotide sequences among individuals.

• Genetic Engineering Review - Image Diversity: DNA fingerprinting

11. Why are recombinant DNA technology and nucleus transplantation technology still dangerous?

Recombinant DNA technology and nucleus transplantation technology (cloning) are extremely dangerous since they are able to modify, in a very short time, the ecological balance that evolution has taken millions of years to create on the planet. During the evolutionary process, under the slow and gradual effect of mutations, genetic recombinations and natural selection, species emerged, were modified, and genetic heritages were formed. With genetic engineering, however, humans can mix and modify genes, making changes with unpredictable long-term consequences, risking the creation of new plant or animal diseases, new types of cancers and new disease outbreaks. It is a field as potentially dangerous as the manipulation of nuclear energy.

12. What is the main moral problem regarding the cloning of human individuals?

In addition to the biological perils, a very serious moral problem involves nucleus transplantation technology concerning humans: the individual rights of a human being are violated when a man or woman is made as a copy of another.

Since it is impossible to first ask if the person to be cloned wants to be a genetic copy of another person or not, it is clear that the most important human right is being violated when making one human as a copy of another: the right to individual freedom. This is a danger to democracy, whose most basic principle is the respect of individual freedom.