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Life as a Machine

Bacteria are a source of many of the tools used in biotechnology. A technique called the polymerase chain reaction, or PCR, made it possible for the first time to amplify tiny starting amounts of DNA and has revolutionised medical diagnosis, testing of IVF embryos for mutations, and forensic science. PCR involves the repeated generation of DNA from a starting sequence in a cycle, one stage of which occurs at boiling point. Because of this PCR uses a DNA polymerase enzyme purified from an ‘extremophile’ bacterium that lives in hot springs. More recently scientists have constructed artificial bacterial or yeast genomes from scratch. The next step will be to create reconfigured bacteria and yeast with enhanced characteristics for use in agriculture, energy production, or generation of new materials. Some scientists are now seeking to expand the genetic code itself. The DNA code that human beings share with all other species on the planet has four ‘letters’, A, C, G, and T, which pair as A:T and C:G to join the two strands of the DNA double helix. And each particular triplet of DNA letters, for instance CGA, or TGC, codes for a specific amino acid, the 20 different amino acids joining together in a specific sequence to make up a particular protein. Scientists have now developed a new DNA letter pair, X:Y. By introducing this into an artificial bacterial genome, it is becoming possible to create many more amino acids than the current 20 naturally occurring ones, and thereby allowing many new types of proteins.