Investigating the Secret of Transmission of Hereditary Traits

DNA, which carries in its folds its own chemical composition, the secret to the transmission of hereditary traits

In the thirties of the 20th century, it became clear to biologists that the secret of the transmission of hereditary traits is in the nucleus of reproductive cells and is associated with chromosomes. But what are chromosomes made of? What is the secret to its installation? How are genetic traits transmitted? The only way that was clear to them at the time was to study the chromosomes under the magnification of a microscope, hoping to increase clarity with higher magnification. However, all this showed them nothing but a complex twisted network of colored filaments centered inside the cell nucleus. It was clear that they needed stronger and clearer magnification than seeing by reflecting light through the lenses of an ordinary light microscope.

Penetrating X-rays

The answer was provided by examining the composition of X-rays and crystals that normally form in inorganic materials. After Wilhelm Konrad Röntgen (1845-1923) discovered the use of X-rays in radiography in 1895, scientists and physicists used them to study. materials and take advantage of their high energy in penetrating Objects. German physicist Max von Laue (1879-1960) discovered the diffraction or scattering of X-rays to study the composition of matter, for which he was awarded the Nobel Prize in Physics in 1914. The first substance whose crystal structure was Table salt was discovered in 1914 by studying X-ray diffraction. Then in the same year, the composition of diamond crystals was discovered. The composition of other materials was later discovered, such as copper, calcium fluoride, iron and titanium ores, and graphite (coal).

The principle of X-ray diffraction imaging of crystals of substances to reveal their composition and to know the arrangement of atoms in their molecular structure

Leading researcher

Dorothy Hodgkin (1910-1994), a pioneer in organic materials research, was born in Cairo and received her academic training at Oxford University in England. He was able to develop a 3D X-ray diffraction imaging method to study the structure of proteins and organic materials.

In 1937, he published the results of his study of the structure of cholesterol, and then he presented his remarkable study that revealed the structure of penicillin in 1946. He discovered the structure of vitamin B12 in 1956 and won the Nobel Prize in Chemistry. in 1964 in recognition of these important pioneering studies. She was the third woman to receive this award. His scientific efforts did not stop, but he continued to study and study until he discovered the composition of the hormone insulin in 1969 after more than thirty years of painstaking research. The X-ray diffraction imaging method became the most important method of scientific research. to study the composition of organic substances and to understand the interactions closely related to their chemical structure.

When Dorothy Hodgkin was 24, she developed rheumatoid arthritis. The disease gradually worsened and led to the disfigurement of his hands, then he became disabled and confined to a wheelchair, but this did not prevent him from continuing his academic studies and teaching at the university. In the 1940s, Margaret Thatcher was one of his students, and when Mrs. Thatcher became Prime Minister, she placed a picture of Dorothy Hodgkin in the office.

Dorothy Hodgkin died at her home of a stroke. He was an outstanding pioneer in the history of chemistry. In addition to being the first British woman to receive the Nobel Prize in Chemistry, Dorothy Hodgkin was the second woman in history to receive the Royal Medal of Honor in 1965, after the famous nurse Florence. Nightingale, who received the award in 1907. Dorothy Hodgkin also received the Lenin Peace Prize from the Soviet Union in 1985.

Dorothy Crowfoot Hodgkin (1910-1994) pioneered the study of the structure of organic matter, along with models of the compounds whose structures she discovered;

Composition of genetic material

Scientists have discovered that chromosomes carry the genetic material and that they consist of special types of nucleic acids and proteins. English physicist and biologist William Thomas Astbury (1898-1961) was able to create the first image of the structure of nucleic acid molecules in genetic material in 1937 using the X-ray diffraction method. These pictures showed that nucleic acids have a regular molecular structure, but he was unable to understand its structure and how it works to transmit hereditary traits.

The famous American scientist Linus Carl Pauling (1901-1994) has been interested in the study of nucleic acids since 1937. Many students of the history of science consider Pauling one of the most important scientists of the twentieth century because of his new. ideas and achievements in many sciences. For example, organic chemistry, mathematics and quantum mechanics. He is also considered one of the founders of quantum chemistry and molecular biology (the science that studies the composition of organic molecules, their modes of action, and their functions in cells and living organisms).

Pauling studied mathematics and quantum mechanics at Oregon State University in America, then traveled to Europe for two years, where he studied with pioneers of quantum physics such as the German Arnold Sommerfeld in Munich, the famous Danish physicist Niels Bohr in Copenhagen, and the Austrian physicist Erwin Schrödinger in Zurich.

Pauling was interested in exploring how to apply the mathematics of quantum mechanics to understanding the electronic structure of atoms and molecules. In 1927, Pauling became an assistant professor of theoretical chemistry at the prestigious scientific institution Caltech (California Science and Research Center). During his first five years there, Pauling published nearly fifty scientific papers on X-ray crystal structure studies and quantitative calculations of atoms and molecules.

In 1930, he received the title of professor. That year, he made a second trip to Europe, during which he learned the method of knowing the composition of materials by studying the deflection of electrons and developed devices for studying the deflection of electrons. and use them to identify the atoms and molecules that make up many chemicals.

Perhaps the most important of his research, which won him the 1954 Nobel Prize in Chemistry, was his extensive study of how atoms are linked together to form molecules of matter and the chemical bonds that make them up. He published his work in 1939 in his famous book, The Nature of the Chemical Bond, which is considered one of the most influential books in the field of chemistry and is still used as a reference in the field more than seventy years after its publication. . In 1962, Pauling was also awarded the Nobel Peace Prize for his political efforts in the field of equality and human rights, making him the only researcher to win the Nobel Prize twice without sharing it, and he became one of only four to have more They received the Nobel Prize. more than once, and the second in two different fields of this prize (the other researcher who won the Nobel Prize in two different fields is Marie Curie, who won the Nobel Prize in physics in 1903 and in chemistry in 1911).

Famous American scientist Linus Carl Pauling Linus Carl Pauling (1901-1994), who won the Nobel Prize twice and led many pioneering studies in the sciences of living cells and genetics

From proteins to nucleic acids

Pauling was the first to describe the structure of the hemoglobin molecule (the hemoglobin that carries oxygen in the blood) and discovered that it changes shape when an oxygen atom is attached to or separated from it. This sparked his curiosity to study the structure of proteins. However, these studies were not easy at the time, as the complex structure of proteins made it difficult to evaluate X-ray diffraction imaging of their molecules. Pauling was able to discover the presence of a characteristic helical turn in some proteins.

He was one of the first pioneers to identify the close relationship between the shape of a protein and its role in vital reactions within the cell, and this was demonstrated in his studies of the function and specific interactions of enzymes (yeasts). Between foreign bodies, such as bacteria, and specific immune antibodies that interact with them.

Thus, in the forties of the twentieth century, it became clear to biologists and geneticists that the chromosomes present in the nucleus of a living cell play an important role in its vital functions, especially in cell division and the transmission of hereditary traits. But how do chromosomes perform these important functions? They knew then that chromosomes contain proteins and long, twisted chains of nucleic acids, and that these nucleic acids have a regular composition of four or five specific types of organic matter, in addition to phosphorus and five. ribose sugar. But what is the exact composition of these nucleic acids? And how does its chemical composition relate to the vital interactions and genetics it carries out?

Race to discover the secret of life

Organic chemists, physicists, and students of the cell sciences raced to answer these important questions because they believed that answering them would open up vast areas for understanding an essential aspect of life’s mysteries: reproduction and heredity. Because these two characteristics are among the main characteristics that distinguish living organisms from other non-living things. Competition and a fierce race between scientists intensified to achieve the chemical structure of genetic material and nucleic acids, but two scientists from the University of Cambridge, Francis Crick and James Watson, were lucky enough to win the race.


Dr. Amer Sheikhoni’s book “The History of Heritage as Discovered by Its People”.

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