Our First Glimpse of the DNA Molecule

 

Our First Glimpse of the DNA Molecule

 The idea of atoms as indivisible particles dates back to ancient Greece. The ancient Greek philosopher Democritus (around 460–370 BCE) proposed the concept of "atomos," suggesting that matter could be divided into indivisible particles. However, this idea was not widely accepted, and it took many centuries for the atomic theory to be revived and developed into the modern atomic theory.

The concept of molecules emerged later in the 19th century. Amedeo Avogadro, an Italian scientist, proposed Avogadro's law in 1811, which stated that equal volumes of gases, at the same temperature and pressure, contain the same number of molecules regardless of their chemical nature and physical properties. This laid the groundwork for understanding molecules as distinct entities.

The development of the atomic and molecular theories was a gradual process, involving contributions from multiple scientists over the centuries. John Dalton's atomic theory in the early 19th century and subsequent advancements in chemistry and physics contributed to our modern understanding of atoms and molecules. The discovery and understanding of atoms and molecules have been ongoing and continue to evolve with scientific research and technological advancements. But no man has ever seen a molecule, let alone an atom untilTop of Form January 1989 when scientists got their first direct look at a very important molecule that changed the biological and medical world.  

For a long time, scientists have been peeping through microscopes at objects too small to be visible through the naked eyes. They have been doing this for four hundred years. The method scientists used was to use lenses that forced light to bend, and in so doing they were able to focus and enlarge images of objects that reflect light. The invention that was able to do this was the microscope.

As the advances in optics progressed over the period, they were able to magnify objects up to 2,000 times as currently with light microscopes. I have several microscopes that are able to do this as microscopy bedsides astronomy is my hobby.

More than 2,000 times, scientists ran into the physical limits of light that comes in waves. Images more than 2,000 times are just magnified without showing further details just like we use a pair of binoculars to magnify trees seen from a distance without being able to see the details of the leaves.

These waves are tiny, but those objects under a microscope were tiny too. If the objects were tinier than the light waves that view them, then the light waves will skip over them so that details of the object could not be seen.

In order to overcome this problem scientists in their ingenuity used shorter light waves such as ultraviolet light. This “ultramicroscopy”, shall we call it temporarily, seems to solve the problem, at least for a while. However, shorter waves could not be focused properly.

In 1923 a French scientist by the name of Louis de Broglie pointed out that subatomic particles exist in wave form too. In 1925 an American scientist named Clinton J. Davisson was able to detect such waves produced by electrons. These electron waves are much shorter than ordinary light waves. They were about the same length as X-rays. But X-rays are extremely difficult to focus, whereas electrons and their waves could be focused easily using magnetic fields.

The first device used to focus electron waves and enlarge the image of objects using this method was constructed in 1932 by a German scientist called Ernest Ruska. This was then the first “electron microscope” which was a crude one initially. However, over the years it was improved and refined until it could magnify up to 300,000 times, a vast improvement over the light microscope that could magnify only up to 2,000 times.

Initially in such a prototype electron microscope the electrons had to pass through an object to produce an enlarged image. This means scientists needed to work with very thin slices of materials for the electrons to pass through. Then they managed to overcome this problem by producing a very thin, sharp beam of electrons and play that beam over the surface by scanning it to produce an enlarged image. This gave rise to the first scanning electron microscope.

Now, a still newer version of electron microscope produced by electrons is called “tunneling effect” and this invention gave rise to a “scanning tunneling electron microscope” that may have reached the limits of its magnification of a million times. This invention gave scientists the ability to peep for the first time ever at a molecule – the molecule of deoxyribonucleic acid (DNA). This was first seen by Miguel B. Salmeron and others at the Lawrence Livermore Laboratory in California in early 1988.

DNA is now so familiar to everyone, even to the non-scientists because it is their chemical footprints of life – you, me and all living creatures that thrive and creep on the surface of this Earth are composed of DNA. Every living cell contains a set of DNA molecules that are constantly replacing themselves, passing the newly created molecules on to daughter cells. Such sets also occur in sperm and egg cells so that they can pass on from parents to children into the generations. Every species of life has their own sets of DNA although there are tiny differences in the sets of different individuals of the same species

But what does DNA matter to life? Its significance to life was first recognized in 1944 that caused scientists to search how these molecules could produce molecules exactly like themselves, somewhat like identical twins.

It was not until 1953 that a British scientist, Francis H.C. Crick, and his American colleague, James D. Watson worked this out. We know that when X-rays pass through molecules they tend to bounce to the side. Photographs of such X-rays produce dots where the X-rays bounce. We call this “X-rays diffraction patterns”. This pattern makes it possible to deduce the shape of molecules. What a beautiful ingenuity of scientists!

 After a long period of time and careful studies they finally found that the DNA molecule consisted of two complex strands of atoms twined together in a double helix like the shape of bedsprings or a winding staircase. They saw each strand had a complicated shape, and the two strands fitted each other precisely.

When DNA forms another molecule like itself, the two strands unwind and each one picks up small groups of atoms from the cell fluid or surrounding area, and puts them together into a new strand that fits exactly upon the original one. In other words, each strand serves as a model to create a new partner for itself. Finally, each DNA molecule produces two DNA molecules exactly alike.

This discovery brought Watson, Crick and another scientist Maurice Wilkins to win the Nobel Prize in Physiology or Medicine in 1962 for their discovery of the molecular structure of DNA, which helped solve one of the most important of all biological riddles. The Nobel Prize for their work was considered a hallmark in very fine scientific reduction. They described the double helix of the DNA molecule so precisely in every detail even though molecules of DNA are far too small.

Thirty years after the discovery of DNA by Watson and Crick, the first picture of the DNA molecules was photographed by the scanning tunnelling electron microscope and no further arguments were required. There was evidence of a double helix so visible to the eyes with the aid of a scanning tunnelling electron microscope. The molecules coil themselves as theoretically expected. From the image it became possible to work out the distance between two successive coils. It turns out to be 5.08 × 10^-6 (0.00,000,508) millimetres – so incredibly small.

Miguel B. Salmeron and his group were planning to refine the method further to see whether they could even see finer details of the strand. The use of the scanning tunnelling electron microscope will enable scientists to look at images of smaller molecules if not atoms. Molecules such as in metals and semiconductors to organic molecules and biological samples are targets of electron microscopy in areas such as molecular immunology in cancer research.

We wish our scientific counterparts every success in their endeavour.