Sunday 4 May 2008

DNA

THE DOUBLE HELIX

“We’ve discovered the secret of life.” Francis Crick, Co-discoverer of the structure of DNA, in local pub, UK, 1953

‘Moreover, the insight that the discovery [of the structure of DNA] provided into how human characteristics arise from our individual genes created a veritable super-highway of research, ushering in gene therapy for inherited diseases and culminating in the recent sequencing of the human genome.’ Adrian Hayday, Professor of Immunobiology, King's College London, UK, 2003
‘DNA is, in every sense, a modern icon. For decades, it has enthralled scientists striving to understand its molecular meaning, provided an aesthetic template for artists, and challenged society with all sorts of ethical conundrums. The defining moment for DNA was the discovery of its structure. Published in the science journal Nature 50 years ago this month, James Watson and Francis Crick described how two strands of DNA embrace to form a double helix, and sparked a scientific revolution. To convince the skeptics that DNA truly was the material of inheritance - the so-called "stuff of life" - it was necessary to show how it could be copied and passed on from one generation to the next. Watson and Crick's model immediately hinted as to how DNA might be copied - each strand of the helix could act as a template to replicate the other.’ Carina Dennis, Nature, from BBC Science, 2003

‘All warm-blooded animals have arisen from one living filament, which THE GREAT FIRST CAUSE endued with animality, with the power of acquiring new parts, attended with new propensities…and thus possessing the faculty of continuing to improve by its own inherent activity, and of delivering those improvement by generation to its posterity, world without end!’ Erasmus Darwin, Zoonomia; or, the Laws of Organic Life, 1, 1794-6

‘DNA – the most interesting molecule in all nature.’ James Watson, Co-discoverer of the structure of DNA

The only media report of the discovery of DNA, the secret of life – in 1953, the same year as Everest was climbed, and Queen Elizabeth 2nd was crowned - was in one newspaper, the News Chronicle.

WEE DNA STORY - ‘A remarkably short scientific paper, known officially as a letter, was published on 25 April 1953 in Nature, by James Watson and Francis Crick. It was perhaps the most momentous paper of the modern era, proposing a structure for the chemical, DNA (Deoxyribose Nucleic Acid), which composes the hereditary material of all living cellular organisms. The proposed structure - a double helix - rapidly became an icon, aesthetically beautiful, and stunning in its capacity to explain how DNA is replicated in order to transmit the genetic material to the next generation…Watson and Crick's paper was published without their undertaking a single experiment. Instead, the experiments underpinning their albeit inspired models were undertaken over the previous three years in the Strand basement laboratories of the Medical Research Council Biophysics Unit at King's. The prime movers in obtaining the data at King's were Professor Maurice Wilkins, who had commenced pilot studies on the use of X-rays to analyse DNA structure, and Dr Rosalind Franklin, a Fellow who arrived at King's in January 1951, and who advanced the X-ray resolution of DNA structure to a new level of clarity and sophistication. Their data were published alongside the Watson and Crick paper but because neither provided a compelling model for DNA structure, they have often been overlooked. In 1962 Wilkins shared the Nobel Prize with Watson and Crick but Franklin had tragically died a few years earlier at the age of 37.’ Adrian Hayday, Professor of Immunobiology, King's College London, UK, 2003

‘All living things reproduce; reproduction, or ‘replication’, is one of the distinguishing features of life. The easiest way to reproduce is simply to divide. This is the way DNA replicates itself…The conceptual problems is – or was – that any one body produces many thousands of different proteins, which do hundreds of thousands of different things, but DNA itself seems chemically simple. In fact a DNA molecule has only three basic componenets: a sugar called deoxyribose; a number of phosphorus-containing groups called ‘phosphate radicals’; and a set of four ‘bases’ or ‘nucleotides’ known as adenine (A), cytosine (C), thymine (T), and guanine (G). These four bases provide the only source of variation in the DNA molecule. No wonder biologists thought it was boring, and could not possibly be the stuff of genes. How could such simplicity generate such complexity, and with such precision? But, as always, nature is way ahead of us… the order in which the four bases occure in the DNA molecule provides a ‘code’ that is in principle rich enough to specify all the proteins that any living thing could ever require: an infinity of possibilities.’ Ian Wilmut, The Second Creation, Headline, 2001

‘This is now the bone of my bones, and flesh of my flesh..’ Genesis, 2, The Bible

‘For many years, people who studied genetics thought that DNA wasn't complex enough to contain all of the information needed to make up a genome. DNA acts as the code, but how does it do it?...The function of DNA depends to a large extent on its structure. The discovery of the structure of DNA by James Watson and Francis Crick is one of the most famous scientific discoveries of all time. The two scientists used evidence collected by other scientists, particularly that of Rosalind Franklin and Maurice Wilkins, to deduce the shape of DNA. One of the most important pieces of evidence came from Franklin's experiments of shining X-rays though the DNA molecule and using photographic film to record where the scattered X-rays fall. The shadows on the film can be used to work out where the dense molecules lie. This technique is known as X-ray crystallography….Working out the arrangement of bases in the DNA helix was made easier by 'Chargaff's rules'…Erwin Chargaff was a Czech-American scientist who had noticed that within every DNA molecule, the number of A bases was always the same as the number of T bases, and that the number of C bases was always the same as the number of G bases.’ YourGenome.org

‘These are the generations of the heaven and of the earth when they were created, in the day that the Lord God made the earth and the heavens, And every plant of the field before it was in the earth, and every herb of the field before it grew…’ Genesis 2, The Bible

‘..a vital propery of a gene was that it could be copied exactly for generation after generation, with only occasional mistakes. What we were trying to guess was the general nature of this copying mechanism… of course now that we know the answer, it all seems so completely obvious that no-one nowadays remembers just how puzzling the problem seemed then.’ Francis Crick, Co-discoverer of the structure of DNA, What Mad Pursuit, Weidenfeld & Nicolson, 1989

‘In principle the duplication of DNA is straighforward, yet in execution it is miraculous, although it happens millions of times each second, in each of us.’ Ian Wilmut, scientist

DNA

DNA – or, deoxyribonucleic acid -
a mouthful which should be a poem;

adenine, cytosine, guanine, thymine,
which should be the names of angels -

creative bond of adenine with thymine,
cystosine with guanine; A toT, C to G,

which is love,
as chemistry.

Who is this poet who can write the flower,
burning-ember leopard, in just four letters

clustered into threes; spell lily skin
and spotted fur, peacock tail, scale.

1.8 metres of DNA in each of our cells,
sparkling spiral strings, silver threads -

wound into structures less than a tenth
of a millimetre across, leaving plenty

of room on the head of a pin for angels,
invisibly clustering the space of a seed;

reaching to the Sun and back 600 times,
bundled into 23 chromosomes, paired –

three billion letters planted with genes,
nuggets of DNA, in encrypted verses –

chemical factories with magic and dancing
at the heart - realised script called to life -

creating proteins - amino acids -
which are the shared spoken word

of skin and wing - peacock and goat;
expression, mechanism of holy code

which has written itself out of nothing,
the original miracle found among stars.

Writing deducted, life deduced,
from the blindness of existence;

evidence and imagination beyond bone,
molecules of bone, to the dream of bone -

Maurice Wilkins, Rosalind Franklin’s
X-ray crystallography, which sounds

like it looks for the heart of rubies -
bone of closed stone, bright skeleton

of a diamond (which might resemble
that of a star, starfish or dandelion) -

shining X-rays through the DNA molecule,
catching the scattered pattern, recording as

a ghosthunter’s camera, authored shadows
on the film, showing the dense molecules -

James Watson and Francis Crick dreaming
the Double Helix, orderly flux; the dancing

spiral, alive with love and creativity -
artist’s shape that is neither life nor

chemistry - idea or dream - but all,
synthesised for imagining, pictured

for understanding, practicality -
as e=mc2 is expression, stripped

poem of energy and mass; so a ladder,
elegant and twisting - with something

of a swan’s neck; backboned poles
of alternating sugar and phosphate

groups – attached bases forming rungs
at each waisted twist, loyal partnering

of bases informed by 'Chargaff's rules’ -
Erwin Chargaff, the Czech-American

who noticed that within every DNA molecule,
the number of A bases was always the same

as the number of T; the number of C bases
was always the same as the number of G -

so Watson and Crick suggested each 'rung'
was composed of a pair of bases, joined by

hydrogen bonds, shackles - A always forming
bonds with T; C always forming bonds with G.

“We’ve discovered the secret of life,” shouted Francis
in the local pub - 1953, when the Moon was still aloof,

blue writing of Earth on the black space page unread -
and the Human Genome lay sparkling like the golden

Pharaoh undisturbed. Pattern and concept, sequence,
mechanism – art and beauty of the Double Helix not

a luxury, lucky add-on, but integral, essential, one,
as everything created by its spiral is a work of art –

creation; kinship residing at the heart of the idea,
making, creating - a holy mechanism, copying –

growing, multiplying; and will become the tiger,
leaf or twitching rabbit in the garden; eagle, fly,

or nomad snail – given four billion years, my child;
gene sequence, spun space, the place of the Word -

deoxyribonucleic acid, etching the words of a poem
with informative light and the blank spaces between -

writing on Earth’s wet page, the work of the blue planet;
sketches and drawings of creation, knitted on spiral pins.

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