Exactly 65 years ago, British scientists James Watson and Francis Crick published an article on deciphering the structure of DNA, laying the foundations for a new science - molecular biology. This discovery has changed a lot in the life of mankind. RIA Novosti talks about the properties of the DNA molecule and why it is so important.
In the second half of the 19th century, biology was a very young science. Scientists were just beginning to study the cell, and the concept of heredity, although they had already been formulated by Gregor Mendel, did not receive wide recognition.
In the spring of 1868, a young Swiss physician, Friedrich Miescher, came to the University of Tübingen (Germany) to do scientific work. He intended to find out what substances the cell consists of. For experiments, I chose leukocytes, which are easy to obtain from pus.
By separating the nucleus from protoplasm, proteins, and fats, Miescher discovered a compound with a high phosphorus content. He called this molecule nuclein (“nucleus” in Latin is the nucleus).
This compound exhibited acidic properties, therefore the term "nucleic acid" was coined. Its prefix deoxyribo means that the molecule contains H groups and sugars. Then it turned out that it was actually salt, but the name was not changed.
At the beginning of the 20th century, scientists already knew that a nuclein is a polymer (that is, a very long flexible molecule of repeating units), the units are composed of four nitrogenous bases (adenine, thymine, guanine and cytosine), and the nuclein is contained in chromosomes - compact structures that arise in dividing cells. Their ability to transmit hereditary traits was demonstrated by the American geneticist Thomas Morgan in experiments on fruit flies.
DNA structure.
Promotional video:
The model that explained genes
But what deoxyribonucleic acid, or DNA for short, does in the cell nucleus, was not understood for a long time. It was thought to play some kind of structural role in chromosomes. The units of heredity - genes - were attributed to the protein nature. The breakthrough was made by the American researcher Oswald Avery, who experimentally proved that genetic material is transmitted from bacteria to bacteria through DNA.
It became clear that DNA needed to be studied. But how? At that time, only X-rays were available to scientists. To shine biological molecules through them, they had to crystallize, and this is difficult. Deciphering the structure of protein molecules by X-ray diffraction patterns was carried out at the Cavendish Laboratory (Cambridge, UK). Young researchers James Watson and Francis Crick who worked there did not have their own experimental data on DNA, so they used the radiographs of colleagues from King's College Maurice Wilkins and Rosalind Franklin.
Watson and Crick proposed a model of the structure of DNA that exactly matches the X-ray diffraction patterns: two parallel strands are twisted into a right-hand helix. Each chain is folded by an arbitrary set of nitrogenous bases, strung on the backbone of their sugars and phosphates, and held by hydrogen bonds stretched between the bases. Moreover, adenine combines only with thymine, and guanine - with cytosine. This rule is called the principle of complementarity.
The Watson and Crick model explained the four main functions of DNA: replication of genetic material, its specificity, storage of information in a molecule, and its ability to mutate.
The scientists published their discovery in the journal Nature on April 25, 1953. Ten years later, he and Maurice Wilkins were awarded the Nobel Prize in Biology (Rosalind Franklin died in 1958 from cancer at the age of 37).
“Now, more than half a century later, we can state that the discovery of the structure of DNA played the same role in the development of biology as the discovery of the atomic nucleus in physics. The elucidation of the structure of the atom led to the birth of a new, quantum physics, and the discovery of the structure of DNA led to the birth of a new, molecular biology,”writes Maxim Frank-Kamenetsky, an outstanding geneticist, DNA researcher, author of the book The Most Important Molecule.
Genetic code
Now it remained to find out how this molecule works. It was known that DNA contains instructions for the synthesis of cellular proteins that do all the work in the cell. Proteins are polymers made up of repeating sets (sequences) of amino acids. Moreover, there are only twenty amino acids. Animal species differ from each other by the set of proteins in cells, that is, by different sequences of amino acids. Genetics argued that these sequences are given by genes, which were then believed to serve as the first building blocks of life. But what genes were, no one knew exactly.
The author of the Big Bang theory, physicist Georgy Gamov, an employee of the George Washington University (USA), made it clear. Based on the model of the double-stranded DNA helix by Watson and Crick, he suggested that a gene is a piece of DNA, that is, a certain sequence of links - nucleotides. Since each nucleotide is one of four nitrogenous bases, you just need to figure out how the four elements encode twenty. This was the idea behind the genetic code.
By the early 1960s, it had been established that proteins are synthesized from amino acids in ribosomes, a kind of "factories" inside the cell. To start protein synthesis, an enzyme approaches the DNA, recognizes a specific site at the beginning of the gene, synthesizes a copy of the gene in the form of a small RNA (it is called a template), then a protein is grown from amino acids in the ribosome.
They also found out that the genetic code is three-letter. This means that three nucleotides correspond to one amino acid. The unit of the code was called a codon. In the ribosome, information from mRNA is read codon by codon, sequentially. And each of them corresponds to several amino acids. What does the cipher look like?
Marshall Nirenberg and Heinrich Mattei from the USA answered this question. In 1961, they presented their results for the first time at a biochemical congress in Moscow. By 1967, the genetic code had been completely decoded. It turned out to be universal for all cells of all organisms, which had far-reaching consequences for science.
The discovery of the structure of DNA and the genetic code has completely reoriented biological research. The fact that each individual has a unique DNA sequence has fundamentally changed forensic science. Deciphering the human genome has given anthropologists a completely new method of studying the evolution of our species. The recently invented DNA editor CRISPR-Cas has taken genetic engineering forward a lot. Apparently, this molecule stores the solution to the most pressing problems of mankind: cancer, genetic diseases, aging.
Tatiana Pichugina