The Secret Museum. Molly Oldfield

Чтение книги онлайн.

      I saw the pencil sketch of DNA in the Wellcome Library, on Euston Road, London. The drawing belongs to the Francis Crick archive, which is made up of 2,000 paper files (or 200,000 sides of text/images) amassed by Crick during his career.

      There I met Ross MacFarlane, research officer at the Wellcome Library, and he showed me a selection of its treasures.

      We began with the oldest thing there, the Johnson Papyrus, a piece of a book, or scroll, from the fifth century AD. It was found in Egypt. It is the oldest surviving illustration of a herbal. What’s a herbal? It is a book with names or drawings of plants, usually with information about the plant as well – including its culinary, aromatic, medicinal or hallucinatory powers, and sometimes legends associated with it. In this case, the ancient, precious drawing is of a bluey-green comfrey plant. Below it, in Greek, is an explanation of how the plant can be used for healing. This is how herbalism developed: by trying out plants and seeing how they made you feel. By trial and error the properties and medicinal uses of different plants were discovered and passed on to others.

      We also looked through a diary belonging to Robert McCormick, ship’s surgeon and natural history expert on HMS Beagle. There is no mention of Darwin in the entire diary. Ross suggested McCormick was probably rather cross that Darwin had turned out to be such a natural history know-it-all, as that wasn’t the reason for him being brought on board the Beagle. Darwin joined the expedition late in the day when Fitzroy, the captain, decided he needed someone who knew about geology to come and keep him company, someone, most importantly, who would pay his own way. Darwin fitted the bill. Although I know he wasn’t a real geology pro because I visited the Sedgwick Museum of Earth Sciences in Cambridge – who own Darwin’s rock collection from the Beagle – and they showed me a diary of Sedgwick’s, in which he mentions taking Darwin on a quick expedition to give him a crash course in geology just before he set sail.

      I also looked through an early guide to swimming written by a Cambridge don in Elizabethan England, and a letter written by the antiquarian Sir Hans Sloane, who collected the countless treasures that became the basis for the British Museum collection. In the letter, he talks about a door that leads from his garden into a coffee shop designed as a cabinet of rarities, where he went to chat over coffee with other local pals who were interested in new ideas and discoveries. I wondered whether he would mention chocolate, for he introduced drinking chocolate to Britain in 1687. He didn’t. But you’ve probably tasted something similar to his blend; ‘Sloane’s Milk Chocolate’ recipe eventually passed into the hands of Cadbury’s.

      Then I came to a white file filled with photographs, scientific papers, personal letters and musings. Ross pulled out the sketch. I instantly recognized the spiralling ladder that carries the Earth’s variety of life forms. The image was sketched in 1953, 84 years after Johann Friedrich Miescher discovered DNA in 1869.

      Miescher found out about DNA – which he called nuclein – when, doing a grim-sounding experiment on cell-digesting, he extracted some enzymes from a pig he had bought at a butcher’s and some cells from bandages used by a soldier during the Prussian War, which was going on at the time. He suggested that nuclein might be involved in heredity, but then discounted his own idea, saying it wasn’t possible that one single molecule could account for all the variation seen within species. He thought that would be far too simple.

      So Francis Crick and James Watson, helped by the work of Rosalind Franklin, didn’t discover DNA, but they did work out what it looked like. They struggled to conceptualize the exact shape of the molecule for years, and were helped enormously by Rosalind Franklin’s skill as an x-ray crystallographer.

      Franklin had spent four years researching crystals in Paris before moving back to London to work on investigating the structure of DNA. She was given jam jars full of gooey DNA and began to take x-ray photographs of it.

      Meanwhile in Cambridge, Crick and Watson made a homemade metal model of DNA as a way to represent, in reality, the ideas they were carrying around in their heads. They had several false starts. They made a triple helix in 1951 and invited Franklin to see it, and she pointed out the molecule as they had made it would never hold together. In 1953, after seeing a photograph taken by Franklin, their ideas fell into place. Finally, they got the model right, and made their physical double helix. This sketch was made around the same time: it was part of the process of grappling with exactly what the DNA molecule looks like. When finally the image became crystal clear in their minds, the scientists were ecstatic. Crick said, ‘It is not easy to convey, unless one has experienced it, the dramatic feeling of sudden enlightenment that floods the mind when the right idea finally clinches into place.’

      Crick and Watson published their realization in the 25 April 1953 edition of Nature. The order of the names on the paper (Watson and Crick) was decided by the flip of a coin. The pair went on to win the Nobel Prize for their discovery, along with Dr Maurice Wilkins; Franklin, who had been pivotal to the research, died before the prize was awarded. Hopefully she would also have been honoured with the prize, had she been alive to receive it, for it would not have happened in the same way without her.

      Now we know that a DNA molecule looks like the image in the sketch: a double helix. Every living creature on earth is made up of right-handed spiral shapes like this. The sketch, according to experts at the Wellcome Collection shows a few key features of the molecule. It is right-handed, it has two strands running in opposite directions, and the building blocks of the strands (nucleotides) have one part that forms the backbone of the molecule and another (the base) that sticks out into the middle of the helix to join with a base on the opposite strand. This joining of two bases is essential in order for DNA to pass on genetic information from one generation to the next. That’s quite a lot of information, crucial to our existence on Earth, in one pencil sketch, don’t you think?

      There СКАЧАТЬ