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DNA: What you must know
Adam Rutherford's book Creation aims to tell the entire story of life on earth - its past, present and future. Here Adam gives an over-view of the building block of all life - DNA.
Every living thing on Earth is encoded in DNA. We’ve described around two million extant species, but these are less than 3% of everything that has ever walked, swam, flown, or just grown on Earth. Almost everything that has ever lived is already extinct. The DNA molecule, the code it uses, and the way it translates its code into living tissue has remained the same for the last four billion years, whether you’re a bacteria or a blue whale, since the dawn of life on Earth, most likely in deep-sea hydrothermal vents called white smokers.
DNA is made of a double helix, a twisted ladder. It only ever twists to the right, like a wood screw, never to the left. The rungs are made up of four chemical letters – A, T, C and G. DNA doesn’t actually do anything other than hold the code in those letters, arranged into genes. In living things, it needs to be first read, then translated into working proteins: all life is made of or by proteins. When we first read the human genome – our total 3 billion letters of DNA – we only had around 22,000 genes, fewer than a roundworm.
The double helix shape of DNA was discovered by English genius Francis Crick and brash American James Watson, using data from Rosalind Franklin and Maurice Wilkins. Wilkins, Crick and Watson got the 1962 Nobel for this: Franklin had died of cancer, and Nobels are never issued posthumously. But DNA was first isolated almost a hundred years before. In Germany in 1869, Friedrich Miescher collected pus-soaked bandages from the rotting wounds of soldiers from the Franco-Prussian War. He squeezed out the cells and purified a white substance, but never pursued this line of enquiry again. He called it ‘nuclein’, we call it DNA.
Genetic modification is the transfer of genes from one species to another. It’s possible because all species use the same coded DNA. So once inserted correctly, the cell can’t tell what is host, and what is alien. It was invented in 1973, a kind of genetic remixing. GM is now the basis for effectively all biological and medical research nowadays, as well as huge food industries: it has been estimated that in the US, 3 trillion meals containing GM crops were consumed in the couple of years before 2012.
Lego is the best toy in the world because each block is designed to fit together so you can simply create new things. Genetic engineering evolved into a new field, called ‘Synthetic Biology’ this century, with that Lego mindset at heart. Scientists in the US figured that progress was slow because none of the parts were standardised, so they created a repository containing thousands of pieces of DNA, which were ready to be assembled. Though few have come to fruition yet, these ‘Biobricks’ have been used in designs for cancer treatments, environmental clear-up, to biofuel production and even for creating building materials for terraforming Mars.
Long shelf life
DNA is remarkably stable: we’ve read genomes from history (Richard III’s bones were ID-ed from their Leicester car park grave using DNA), and from prehistory (this week DNA showed that a 7000-year dead man had blue eyes and dark hair). We’ve gone way further back, and read the whole genome of our Neanderthals cousins from more than 40,000 years ago, to reveal facts such as that they were ginger-haired. And, it turned out, that our ancestors were partial to the occasional inter-species hanky panky with the Neanderthals: many of us carry their DNA, and we may have acquired genes involved in diabetes from them. Thanks a lot, cavemen.
It’s a hard drive
Because of that stability, and because DNA is effectively a data format, scientists have begun to use DNA like a hard drive. It’s stable, and won’t ever go the way of the Betamax or Laserdisc, because there won’t ever be a time when we won’t study DNA. `because of its size, the density of data storage is many times higher than Blu-Ray. In 2012, scientists wrote a whole raft of non-living things into DNA. A British team encoded all Shakespeare’s sonnets, and a HD video of Martin Luther King’s ‘I have a dream’ speech. It’s a slow format to write and read currently, but the time is coming when your hard-drive uses the same formatting as your cells.
Evolution got it right just once, inventing a language that was simple but powerful enough to underwrite every species for four billion years. But that doesn’t mean we can’t go one better. The four-letter alphabet in the language of genes has been extended to at least seven. These have been used to create cancer treatments and even bog standard cold sore creams. But Cambridge scientists have begun redesigning the molecules of life so that they can evolve – they call them XNA. One day soon, it will be life, but not as we know it.
Adam Rutherford, for Waterstones.com/blog
You can Reserve & Collect Creation: The Origin of Life / The Future of Life from your local Waterstones bookshop (http://bit.ly/1jkkuin), buy it online at Waterstones.com (http://bit.ly/1jkktek) or download it in ePub format (http://bit.ly/1jkkv5S)