31.1 Concept Check
The techniques of genetic engineering are based on fundamental discoveries in molecular genetics and biochemistry. Successful genetic engineering depends not only on being able to carry out molecular cloning, but also knowledge of replication, transcription, and translation.
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31.2 Concept Check
Molecular cloning requires a cell or organism to serve as the host for the cloned DNA. In biotechnology, the choice of a host depends on the final application. In many cases the host can be a prokaryote, but in others it is essential that the host be eukaryotic. To serve as a host it is necessary for the cell or organism to take up DNA, and there are a variety of techniques by which this can be accomplished.
31.3 Concept Check
Special procedures are needed for detecting the foreign gene in the cloning host. If the gene is expressed, the presence of the foreign protein itself, as detected either by its activity or by reaction with specific antibodies, is evidence that the gene is present. However, if the gene is not expressed, then its presence can be detected by use of a nucleic acid probe.
31.4 Concept Check
Many cloned genes will not normally be expressed efficiently in a new host. Expression vectors have been developed that contain a variety of genes or portions of genes that will increase the level of transcription of the cloned gene and make its transcription subject to specific regulation. Signals to improve the efficiency of translation may also be present in the expression vector. Expression vectors and other specialized vectors have been developed for both prokaryotic and eukaryotic hosts.
31.5 Concept Check
It is possible to achieve very high levels of expression of mammalian genes in Bacteria. However, these genes are almost invariably different from the native gene, as it is essential that it contain no introns. This can be accomplished by using reverse transcriptase to synthesize complementary DNA (cDNA) from messenger RNA (mRNA). It can also be accomplished by synthesizing an entirely synthetic gene using the knowledge of the amino acid sequence of the protein one wishes it to encode.
31.6 Concept Check
The first human protein made commercially using engineered bacteria was human insulin, but numerous other hormones and other human proteins are now being produced. Many proteins found in humans that were formerly extremely expensive to produce because they were found in human tissues in only small amounts can now be made in very large amounts from the cloned gene in a suitable expression system. In addition to useful pharmaceuticals such as anticancer agents and immune modulators, even vaccines can be produced using genetic engineering.
31.7 Concept Check
Genetic engineering is being employed to make plants resistant to disease, to improve product quality, and to use crop plants as a source of recombinant proteins and even vaccines. One commonly used cloning vector for plants is the Ti plasmid of the bacterium Agrobacterium tumefaciens. This plasmid can transfer DNA into plant cells. Plants whose genomes have been modified using in vitro genetic techniques are called genetically modified organisms or GMOs.
31.8 Concept Check
Genetic engineering can be used to develop transgenic animals capable of producing proteins of pharmaceutical value. The techniques of genetic engineering are also applied to identifying individuals using DNA fingerprinting. One of the great promises of genetic engineering is gene therapy, where functional copies of a gene can be supplied to an individual to treat human genetic disease.