In the modern scientific community, there are several theories about the method of transmitting information from parents to descendants: from wave to futuristic type of supermind groups. However, the fact that it is DNA molecules that are the material basis for the continuity of organisms does not cause controversy. Understanding how evidence has been formed in the scientific community about the genetic role of DNA and what they are is the purpose of this article.
A bit of theory for non biologists
To understand the subject and the very essence of the proof of the role of DNA in heredity, we recall only some general concepts and terms used in the text. Molecular biologists and other professional biologists may not read this part - concepts are given in a simplified version for the interested part of readers. Although the modern specialization in biology today has grown so much that a professional environmentalist will not always break through to understanding the essence of evolutionary mechanisms, and the specifics of the development of a frog embryo are not unambiguously understood by botanists. So, these are the terms:
- DNA (deoxyribonucleic acid) and RNA (ribonucleic acid) are long and large molecules consisting of monomers - nucleotides.
- DNA and RNA are called nucleic acids.
- DNA and RNA are formed by only four nucleotides (three identical, one different in DNA and RNA) - nucleotides are universal for all living things on the planet. These are complex organic compounds from a nitrogenous base, a carbohydrate residue, and phosphoric acid. They are called adein, guanine, thymine and cytosine (uracil).
- Nucleotides form triplets - they encode one amino acid out of twenty.
- Triplets form chains in the composition of nucleic acids, which corresponds to a chain of amino acids or one specific protein. Proteins are the basis of life on the planet, they are specific and unique.
- A gene is a piece of nucleic acid that is responsible for one protein.
- Genome - the totality of all the genetic material of the body.
A bit of history
The Swiss biologist F. Miescher in 1869 saw chains in the nuclei of pus cells (leukocytes), which he called nucleic acids.
German A. Kassel as a biochemist calculated their composition: sugar, phosphoric acid and five varieties of nitrogenous bases. He in 1891 proved that there are two nucleic acids - DNA and RNA. In the period from these discoveries until 1953, studies were conducted on the chemical composition and structural organization of nucleic acids. Famous surnames of this period are F. Leuven, A. Todd, E. Chargaff. The experiments begun by F. Griffith (1928) and continued by O. Avery, C. MacLeod, and M. McCarthy (1944), provided evidence of the role of DNA in the transfer of genetic information, more on that later. In 1953, Americans J. Watson and F. Crick proposed a model of the DNA structure in the form of a double twisted helix, which was even known to a student. That's it, molecular biology was born!
From protein to DNA
At that point in time, nucleic acids seemed like strange material in the nucleus of a cell. For what these formations are needed, they did not know, and even less did not look for evidence of the genetic role of nucleic acids. Proteins consisting of amino acids and having a more complex chemical structure have already been discovered. It was proteins that were considered carriers of hereditary information.
The material that carries hereditary information was the first to doubt the English bacteriologist F. Griffith in 1928. And although he could not provide convincing evidence of the genetic role of DNA, his experiments deserve attention.
Griffith pneumococcal strains
Frederick Griffith, a bacteriologist from England, infected mice with Pneutnococcus pneumoniae viruses, which caused pneumonia in them, and the animals died. Pneumococci exist in two forms - infectious (virulent) and non-infectious (avirulent). These forms are easy to distinguish. Virulent pneumococcus has a mucopolysaccharide capsule that protects the cell. Avirulent capsules do not have and cannot defend themselves against mouse immune cells; therefore, mice do not develop pneumonia. The postulate of that time: heated virulent pneumococcus becomes avirulent. A biologist infects mice with a mixture of a heated virulent strain and live avirulent (capsule-free). The mice are dying. In their bodies, the scientist discovers live pneumococci with a capsule shell. Griffith’s conclusion: from dead virulent pneumococci to living, but capsule-free forms, something is transmitted (a “transforming agent”) that “transforms” avirulent forms into virulent ones with a fixed attribute as hereditary (pneumococci multiply rapidly: those that he found in corpses mice - the hundredth generation of the first). And since viruses have nothing in structure except nucleic acids (DNA and RNA), it is actually F. Griffith who owns the first evidence of the genetic role of DNA and RNA, although he called them the “transforming agent”. Recall that this happened in 1928.
Experimental evidence for the role of DNA in information transfer
Almost the same thing that Griffith did, only without poor mice, was done in 1944 by O. T. Avery, K. M. MacLeod, and M. McCarthy. At the Rockefeller Institute for Medical Research in New York, they obtained in vitro (in vitro) a pure Griffith transforming agent from killed virulent forms and mixed it, again in vitro, with avirulent forms. Received encapsulated pathogens. And then we studied the composition of this same agent. At first, they proved that it was not protein, and that in itself was already an innovation. Well, then they came to the conclusion that this agent is nucleic acid. These American experiments are direct evidence of the genetic role of DNA in the transmission of hereditary information. But not the only ones that science considers classics.
The second of the classic evidence for the genetic role of DNA
The first we have already described - these are the experiments of Avery - MacLeod - M. McCarthy.
Classics of biology - two more experiments as direct evidence of the genetic role of DNA. The description is reduced to the point.
American geneticist Alfred Hershey received the Nobel Prize (1969) for these experiments. An interesting series of experiments by Hershey and Martha Chase, conducted in 1952 at the University of Washington in St. Louis with bacteria and bacteriophages labeled with radioactive phosphorus and sulfur. Their findings that it is bacteriophage DNA that penetrates bacteria and gives rise to new bacteriophages is a classic proof of the genetic role of DNA.
Third experience
The German-American biochemist Heinz Ludwig Frenkel-Konrat received the Lasker Prize (1958) for his research. At the University of California in 1957, he conducted experiments with the tobacco mosaic virus. Their scheme is similar to the Griffith ones. His achievement is that he proved the participation of RNA in the transmission of hereditary information.
Interesting modern evidence
Modern molecular biology and genetics constantly provide us with new evidence of the genetic role of DNA. Some very interesting, unexpected and impressive facts from studies of modern science, which in one way or another prove the role of DNA in the formation of an organism, are given below.
In 2007, scientists were able to isolate a portion of the DNA of amphibians, which is responsible for the formation of the eye. Today there are already salamanders with eyes on their feet and tail.
In the genome of goats, scientists have implanted the spider gene responsible for the web protein, as a result of this protein appeared in the milk of goats. After special processing and extraction of protein from milk, spider silk is formed.
The Dutch raised cows with the human gene responsible for a specific milk protein of women - lactoferrin. This protein plays an important role in the primary immunity of infants. Testing of cow's milk continues, but the prospects for its use in medicine are impressive.
Supplementing the piglet embryo gene with the fluorescent jellyfish protein gene, Chinese scientists have grown two green-lit piglets.
In 2008, the world spread the news of the birth of a child with an artificially modified genome. This happened in London, where a woman agreed to an experiment because of the discovered genetic abnormalities in the genome of the embryo.
Human chimeras exist. In a 2002 DNA test for paternity, a test showed that American Lydia Fairchild is not the mother of her unborn child. Studies repeated, but analysis showed the same results. It turned out that Lydia's body developed from two eggs, fertilized by different sperm and merged in the early stages of ontogenesis. Therefore, her body consists of tissues and cells with a different set of chromosomes.
Everyone knows about DNA testing for paternity or in judicial practice. But DNA tests are also used to verify products for authenticity. For example, you can set a gathering place for caviar or grapes for fine wine.
There are 4 families in the world whose members do not have fingerprints. Adermatoglyphia is caused by a rare mutation of a single gene.
The alternation of sleep and wakefulness in humans controls the hDEC2 gene; its mutation reduces the need for sleep to 4 hours.
Cryogenetics has been successful in cloning a mouse that has been frozen for 16 years. Scientists have not learned to revive the "polar explorers", but you can clone them.
And a little about the most unique molecule
- 10 billion kilometers, from earth to Pluto and vice versa - this is the length of human DNA, if decomposed.
- It is possible to print the entire human genome at a speed of 8 characters per second, working 8 hours a day, for 50 years.
- All the information in the world that is stored in digital format can fit in two grams of DNA.
- On the "immortal" hard drive stored at the space station, in the event of a disaster, the DNA of famous people, including Stephen Hawking and Lance Armstrong, is placed.
- In each cell of our body, each DNA molecule undergoes various damages about a million times a day. However, we are still alive - oh, a miracle!
Summarize
Despite the successes of molecular biology and our knowledge of DNA, mankind does not yet know the answers to many questions. Who knows what discoveries await us in the future, will mankind get rid of hereditary diseases and will aging be defeated ...