Scientists 'see' DNA structure clearly for first time


WASHINGTON -- Scientists reported Thursday they have produced the first direct picture of the DNA molecule, giving researchers their most detailed glimpse of the material that is the genetic blueprint for all life.

In findings published in the journal Science, a team of California researchers said by using a scanning tunneling microscope, which can record structural details of things as small as an atom, they were able to capture the first good image of DNA's double helix structure magnified 1 million times.


Deoxyribonucleic acid, or DNA, a large molecule found mainly in the chromosome of a cell, is the carrier of genetic information in plants and animals. Humans have 46 chromosomes, and babies receive half of their chromosomes from their mother and half from their father.

'This is the first high-resolution picture where you can see the detailed, twisting structure within a DNA molecule,' said Rod Balhorn, a biochemist who was part of the team from Lawrence Livermore National Laboratory and Lawrence Berkeley Laboratory near San Francisco.

In the past, scientists working with DNA have had to rely on models, patterns of chemical binding or on 'shadow' images created by bouncing X-rays off the genetic material. Previous attempts to use the scanning tunneling microscope on DNA have produced fuzzy images.


'Ever since (James) Watson and (Francis) Crick proposed the structure of the DNA molecule (in 1953), everything has depended on deduction without actually being able to see it,' he said.

Balhorn said the scanning tunneling microscope is able to produce a three-dimensional picture of small objects through an electronic technique similar to a finger feeling the raised dots of Braille.

The most immediate beneficiary of the new images is expected to be the human genome project -- a massive effort to map and decipher every gene in the human body. The proposed federal budget for 1990 calls for giving the National Institutes of Health $100 million for that project.

The ability to 'see' DNA molecules may also help to speed up the work of researchers attempting to find specific genetic markers for diseases such as cancer, diabetes and epilepsy, and those trying to figure out how genetic damage occurs.

Balhorn said the trick to getting clear pictures of DNA's complex structure is making the tip of the microscope's scanning needle as sharp as possible. 'It has to be sharp down to a single atom,' he said, adding researchers still cannot produce high-quality images of DNA on a fast, consistent basis.


Although the new pictures turned up no big surprises, Balhorn said the images support recent theories that DNA's structure is not always uniform, and can vary along the length of a chromosome.

Balhorn said the California findings have recently been duplicated by a couple of other laboratories. He estimated there are about 100 scanning tunneling microscopes in the world.

'In general, it is a very simple instrument that is relatively inexpensive compared to other scientific equipment,' he said. 'Since we've shown it can be used to image biological molecules, I believe its use will blossom.'

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