Recombinant cloning combines DNA sequences not found naturally, often using bacteria and a vector like a plasmid. Restriction endonucleases cut and recombine DNA, allowing for gene expression and large-scale protein production. There are practical applications, but some uses are controversial.
Recombinant cloning usually refers to recombinant DNA techniques. This involves combining DNA sequences that would not exist naturally. These techniques are also sometimes called genetic engineering. Specific segments of DNA are isolated and combined into a smaller DNA unit that will replicate and amplify the number of cloned DNA molecules.
Host organisms for recombinant cloning are often bacteria. The DNA vehicle used for cloning is known as a vector and is usually a virus or plasmid, a circular piece of bacterial DNA found outside the bacterial chromosome. A plasmid for cloning will have an origin of replication so it can replicate, a cloning site, and some sort of selectable marker, such as antibiotic resistance. This will ensure selection and propagation of cells containing the clone.
The cloning site has a specialized sequence that will be recognized by a particular restriction endonuclease, an enzyme that recognizes specific DNA sequences and cuts nucleotides. The plasmid will first be cut, so that it is linear. Researchers generally try to use restriction endonucleases that leave overlapping “sticky ends” and annealing the ends of the target gene with compatible sequences in the vector using ligase, thus restoring it back to a circle. Once the gene has been cloned into the vector, the vector is introduced into its host of expression, usually by a process known as transformation, and grown in large numbers. The DNA can then be isolated and used in experiments.
Recombinant cloning has allowed the analysis of large quantities of molecules that are normally only transiently expressed in the cell, such as mRNAs and proteins. This revolutionized the study of biology. There are many practical applications of recombinant cloning.
Proteins such as human growth hormone can be expressed in large quantities through recombinant cloning. Transgenic plants are used in agriculture to prevent the attack of insects and pathogens. Many foods have been genetically modified to improve them, and cows have been treated with bovine growth hormone produced by recombinant cloning to increase milk production. Gene therapy has been used in many therapies, including to treat a form of blindness. Animals are even cloned, although the clones often suffer from health problems.
Some uses of recombinant cloning are highly controversial. Many people are against eating genetically modified foods or drinking milk containing recombinant hormones. There is much concern that GM crops could spread their new genes into local flora.
Some people are philosophically against altering existing life forms. There is almost universal condemnation of the idea of human cloning. Whether these new technologies will reach their full practical potential or whether society will limit their use remains to be seen.
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