Concepts: Principles of biotechnology

1.1 Two meanings of one word

In the broad sense, biotechnology covers any technique that uses living organisms, cells or enzymes from them to make products and processes useful to people. Curd making, baking and brewing all fit that description because microbes do the work. Modern usage is narrower: it covers work that uses genetically modified organisms to do the same jobs on a much bigger scale. The subject also takes in in vitro fertilisation and the test tube baby, the synthesis and use of a gene, DNA vaccines and the correction of a defective gene.

The European Federation of Biotechnology frames the subject as the bringing together of natural science with living things, their cells and components, and molecular analogues, all aimed at products and services. That wording keeps the old food fermentations and the new molecular work inside one field. In practice the two sit side by side: a curd maker and a company that expresses a human gene in bacteria both use living cells, but only the second changes the DNA first.

1.2 The two techniques that started modern biotechnology

Genetic engineering rewrites the chemistry of DNA and RNA, moves the changed material into a host organism, and in that way alters the host's phenotype. Bioprocess engineering keeps the surroundings sterile, free of microbial contamination, during chemical engineering steps, so that only the desired microbe or eukaryotic cell grows, and grows in large numbers, for products such as antibiotics, vaccines and enzymes.

1.3 Why recombinant DNA was needed

Sexual reproduction creates variation by mixing genomes, and some of the new combinations help the organism and the population. Asexual reproduction preserves an existing genome without change. Plant and animal breeders long used hybridisation to combine useful traits, but the method drags along unwanted genes that come with the desired ones. Creating recombinant DNA, cloning genes and transferring genes lets a breeder isolate one gene, or a small set of genes, and move only those into the target organism.

1.4 Why an alien DNA needs an origin of replication

A piece of DNA slipped into a foreign organism usually fails to multiply in the recipient's progeny. It does replicate once it becomes part of the recipient's genome, because a chromosome carries the ability to copy itself. Inside every chromosome is a specific sequence called the origin of replication, or ori, where copying begins. Any alien DNA therefore has to be joined to a sequence of this kind if it is to multiply inside the host. Linking a gene to an ori turns the gene into a replicating unit, and making many identical copies of a template DNA is what we call cloning.

1.5 The first artificial recombinant DNA

Stanley Cohen and Herbert Boyer produced the first artificial recombinant DNA in 1972. They cut out a piece of DNA carrying an antibiotic resistance gene from a plasmid and linked it to a native plasmid of Salmonella typhimurium. The cutting was possible because restriction enzymes had just been found. The cut pieces were joined by DNA ligase, which acts on cut DNA and seals the ends, and the plasmid carried the new piece as a vector. The recombinant molecule was introduced into Escherichia coli, a close relative of Salmonella, where it copied itself using the host's DNA polymerase and produced many copies. The experiment became the founding moment of the discipline. What made the experiment a turning point was the combination: a precise cut, a carrier molecule and a host that copied the new DNA. None of the three pieces was new on its own, but together they made gene transfer a routine operation.

Three basic steps sit inside every attempt to modify an organism genetically. First, identify the DNA that carries the desired gene. Second, get that DNA into the host. Third, keep the DNA in the host and pass it on to the host's progeny.

1.6 Exam pointers

A common mistake is to write that a foreign gene replicates on its own; it replicates only after it is joined to a chromosome or to an ori-bearing vector. Another is to give recombinant DNA technology credit only for medicine, when its stated advantage is precise gene transfer. For the history question, keep the order clear: restriction enzymes and ligase came first as tools, Cohen and Boyer used them in 1972, and E. coli expressed the cloned gene.