Academician Eric Galimov, a famous geochemist, creator of the theory of isotope biological fractionation, the author of works on the genesis of planets and the Moon, isotope chemistry, geology and geochemistry of oil and gas, formation of diamonds, Director of the RAS Institute of Geochemistry and Analytical Chemistry named after Vladimir Vernadsky, has propounded an original hypothesis on the origin of life, the laws of its evolution and the mechanism of genetic code emergence. Our correspondent Igor Goryunov asked the scientist to comment on some of his conceptual points.
- Eric Mikhailovich, it has been 50 years since the would-be Nobel Prizewinners American James Watson and Englishman Francis Crick found the DNA structure. How did scientists profit by the discovery of the double helix of deoxyribonucleic acid? How did this event affect the progress of science in the twentieth century?
- Their DNA model is one of the most remarkable scientific discoveries of the past century. It has elucidated the molecular mechanism of heredity. Pretty soon afterwards the genetic code was deciphered. Life chemistry is controlled by enzyme proteins. They consist of amino-
Articles in this rubric reflect the opinion of the author. - Ed.
acids. Each of those is matched by nucleotides. Its long chain stores the composition of all proteins that an organism is to produce in order to sustain vital functions. However, the basic question still awaits an answer: how did nature arrive at the "idea" of programming? How was the genetic code created?
To resolve this problem is as good as to answer the question of the origin of life: to trigger the evolution process, all the Creator had to do was to indicate the genetic code.
- It appears, someone has created it deliberately?
- That's what some scientists believe. E.g., the American M. Beche proves: the molecular mechanism of life could have appeared only at the Creator's will. Even Crick himself who not just discovered the DNA structure but made a great contribution to the deciphering of the genetic code, at the end of his scientific career started to talk about panspermia, i.e., the extraterrestrial origin of life on earth.
- In other words, the origin of genetic code is a mystery? What is your view of the ways to resolve this scientific problem ?
- Let me say first: I believe that the genesis and evolution of life is a normal physico- chemical process developing on planets in conditions similar to those that existed of the young Earth, i.e., 200 - 300 million years after its formation (today the Earth is believed to be almost 4.7 billion years old).
So, what is the mechanism of the appearance of life and what keeps the evolution going? It might seem that the question has long been given a generally accepted answer: Darwin's natural selection. True, when we are discussing the mechanisms of adaptation to natural environment or biological diversity, Darwinism works, and I could give numerous examples to confirm its correctness. But it does not help to understand the way life originated, since it is not the general theory of matter organization which we usually associate with complication. And not just with that. Ordering also presupposes the restriction of freedom, some rules of behavior. Say, street traffic is regulated by a whole number of constraints: division lines, control lights, signs and so forth. The same happens in chemistry. If three separate amino- acids form a peptide, that means ordering, since in this more complex structure aminoacids cannot behave in space as freely as in isolated existence. In turn, the generated peptide introduces organization into the environment. Moreover, it is able to act as a catalyzer in other reactions.
- So, catalyzers are essentially agents of ordering in nature ?
- Yes. It's common knowledge that any catalyzer is an accelerator of some process. But it is capable of that because it selects a certain mode most beneficial from the perspective of reaction speed. Therefore, a catalyzer, primarily, performs a selection function.
Proteins are present-day biocat-alyzers (enzymes). Each of them controls just one and only one reaction, and together they form an intricate "machine".
Of all chemical compounds we know there are no better catalyzers that aminoacid polymers. They form a three-dimensional structure
The Darwinian evolution.
Evolutionary law of stationary systems (according to E. Galimov).
Three-dimensional image of an RNA molecule.
which possesses most perfect selective properties, i.e., is effective at ordering.
- Let's get back to the mechanism of organization. That is true that rules of traffic introduce order into movement on roads, but they are specially designed, and you say that in the Universe such rules develop spontaneously ?
- In accordance with the general law of nature known as the second law of thermodynamics, the most natural trend of matter evolution is that of disordering (increase of entropy). It reaches maximum in the state of equilibrium where no visible changes take place-the system is dead. To reverse the natural trend of the matter, a few conditions should be met. First of all, a reaction instrumenting ordering (i.e., flowing with entropy decrease) should be integrated at a microscopic level (actually forming the integral whole) with a reaction developing with the increase of entropy. Further, the system should be stationary: the decrease of any component within the system should be offset by its reproduction. And that requires a continuous inflow of energy from the outside. None of the above factors is anything extraordinary, examples of such organization in nature are common.
I believe that in prebiotic chemistry a special role was performed by adenosine triphosphate (ATP) molecules. Their hydrolysis perfectly matches the ordering requirements. Although rather complex, these molecules are nevertheless synthesized of simple precursors: hydrogen cyanide, formaldehyde and phosphates, the compounds available in the early phases of our planet's evolution. This process presupposes a certain geochemical scenario, but, for all we know of the conditions at that time, its realization looks quite plausible. For the special role I attach ATP in prebiotic chemistry, it might be termed "molecule No. 1" in the path of biological evolution.
By the way, ATP is very important for contemporary living organisms too. This is a proof of its early origin, since Mother Nature, having once found some original solution, tries to replicate it in a maximum possible number of options, rather than invent something new.
However, the ordering process alone cannot explain evolution: in each phase it's just a particular case. To complete the picture, the organized structure should be able to copy itself, or sooner or later it will perish. Besides, initially, ordering could be realized in the synthesis of one molecule only. To translate this microscopic event into a macroscopic result, a mechanism of reproduction was needed. And a large quantity of one and the same structure may be obtained in two ways: either by making each specimen from scratch independently from one another, or by copying the first mold. The performance difference is like that between hand-copying of ancient manuscripts and contemporary photo-copying.
As I said, aminoacid chains (pep-tides) have the property of ordering but not self- reproduction. Conversely, nucleotides are poor catalyzers, but due to their ability to build complementary chains they can splendidly reproduce. In other words, for objective reasons related to organic chemistry, the two properties essential for ordering evolution proved to be split between two different classes of compounds. And the genetic code is the very program responsible for the match between the structural elements of one class (aminoacids) and those of another (nucleotides). As a result, aminoacids can reproduce through the medium of nucleotide chains.
The evolution is effected by two interconnected processes. The first is ordering, the second-reproduction (iteration) of already organized structures. I prefer the term "iteration", because reproduction is an exact copying, and iteration implies production of duplicates much similar to the original.
- Why is exact copying impossible? Are there any limitations?
- Laws of nature which prevent the production of an analog. But that is not required. Even if iteration does not reproduce the exact copy, it will still be viable. Moreover, from the standpoint of evolution, a mismatch with the original opens up new opportunities, since the duplicate may possess even better adaptability.
- Your logical construction of genetic code origination is clear. And how does it work in reality ?
- A specific way of genetic code evolvement is still to be discovered. To explain it numerous hypotheses have been propounded. From the standpoint of our approach, I prefer those which suggest consecutive ordering through increasingly strict match between an aminoacid and a set of nucleotides. In the present organisms the mechanism of transcription (rewriting) is extremely complex. And the central role in it is played by transfer RNA. Back in 1958 Crick propounded that there should exist an intermediary molecule connecting a specific aminoacid with a certain set of nucleotides. Later it was identified as transfer RNA.
Although at the dawn of biological systems' evolution an analog of genetic code, as compared to the presently existing, was simplistic and unreliable, transfer RNA and similar archaic structures, unlike other nucleic acids performing biological functions, were and still are relatively short formations containing only 70 - 90 nucleotides, in which they resembled polynucleotides which had formed before the appearance of the code. In fact, polynucleotides synthesized experimentally this day have just the structure of transfer RNA. Usually, these are intricately rolled chains in which a sequence of nucleotides forms pairs of complementary bases. The primordial nature of transfer RNA is also evidenced by the fact that it contains a more diversified set of nucleic bases than DNA or RNA.
Apparently, the purging of RNA and DNA of superfluous nucleotide structural forms took place in the course of evolution.
By its significance and the place it occupies in biological evolution, prototransfer RNA is "molecule No. 2". It proved to be an intermediary between aminoacids and nucleotides.
- Is there a way to verify your hypothesis? Are you planning any experiments?
- Yes. RAS has adopted as a priority the program called "Problem of the Origin and Evolution of Life". Within its framework our institute and some other organizations (we are planning to cooperate with scientists of Moscow State University named after M. Lomonosov, RAS institutes of biological sciences and the RAS Siberian Branch) will conduct experiments to test the ATP role in the ordering mechanism, ATP synthesis in conditions simulating the primordial earthly environment.
- What about testing the concept of genetic code origin?
- At a glance it might seem that the dramatic experiment to demonstrate the mechanism of genetic code origination can be carried out on a laboratory bench. But a spontaneous matching is an extremely lengthy process. Even if we knew its every detail with absolute accuracy, still its reconstruction would occupy millennia.
But the process may be accelerated millions of times if modeled by computer simulation. Presently we are actively working on that with my colleague Vasily Dementyev, Dr. Sc. (Phys. & Math.). We want to make sure that if we formalize our understanding of the ordering nature in a certain way, its mechanism will inevitably come across the idea of genetic code.
- What mathematical apparatus is required for such work? Can you use an off- the-shelf one or will you have to create something new?
- Now we are carrying on numeric experiments in a code language,
The initial phase of evolution according to Eric Galimov.
although computer simulation of the life origination process should be conducted in terms of quantum chemistry. But to use the apparatus of that science, we first need to get a certain result at least in a code language-some option of the origin of life. To be sure, we cannot maintain that the type of life realized on earth is the only possible, but it is one of a very limited number of options. In other words, if life exists elsewhere in the Universe (and I believe that it must exist in whatever form and is not infrequent), in its main features it should resemble the terrestrial life. Any intelligent creature from another planet is sure to be like us. It may have a different appearance, body structure, but the basis of the vital processes will be laid by the same proteins, the same data recording with the help of nucleic acids, etc. Moreover, the Universe simply has no other elements than carbon and hydrogen to build life upon. It is only carbon that allows to build linear chains, rings, form double bonds. And the only element similar to it-silicon-is unable to build double chains. Similarly, hydrogen playing an enormous role, e.g., in replication (reproduction), has no substitutes either. Therefore, in the organization of life much is predetermined: with the apparent diversity, there's a limited set of compounds available for its construction.
- Nevertheless, it is often propounded nowadays that somewhere exists a virtual life, without material incarnation...
- The notions of virtual, computer or similar creatures seem to be unfounded fantasies. In fact, the appearance of living creatures is only possible on the basis of the elements available in terrestrial conditions. As I said, they are but few.
- Are there limits of life? Did you put that question?
- To be sure, anything living has its beginning and its end, the more so if we view biological evolution as a self-developing process of ordering. Any complex structure after some time passes into the state of disorder. And life contains inherent features which predetermine its collapse into chaos. First, remember iteration: as copies are reproduced, any smallest error or uncertainty is magnified in the further process, therefore its end result is practically unpredictable. Second, biological processes have an element of non-linearity-the dependence of rules controlling the iteration process on the result. These speculations are rather of philosophic nature, and I as a geochemist studying the process of living matter synthesis in the real historical context have to inadvertently resort to some generalizations.
Generally speaking, the problem of the origin of life (and now we are concerned with its beginning, not the end) can be addressed both from the natural-science and philosophic perspectives. By philosophy I imply the level of generalization maximally possible for the given phase of human civilization, including scientific generalization. And when mind runs into a blind alley, well, to
Diagram of formation of ATP-key molecule of pre-biological synthesis on early Earth (according to E. Galimov hypothesis).
get out of the impasse we have to change the very philosophy. So, in my opinion, philosophic reflexion should, on the one hand, forerun scientific analysis setting the vector of research, and on the other-introduce corrections into an achieved knowledge, update the existing concepts, if they prove to be productive, or put forward new ones stating new problems and posing new questions. Along with philosophy, religion is another yardstick of human intellectual and spiritual development. But it should constantly evolve too, to match the level of contemporary concept of the Universe, certainly, within the framework of its paradigm. Say, thunder and lightning were once associated with the chariots of gods. At that time the outlook that incorporated the notion of Zeus riding in the skies had the right to existence. But as soon as science discovered the nature of electric discharges, the habitual explanations became inadequate and religion has discarded them.
- Academician Vladimir Vernadsky said that religion is very much interested in the progress of science, and vice versa: "The growth of science, in turn, inevitably invokes an unprecedented expansion of the boundaries of philosophic and religious conceptions of human spirit; religion and philosophy, having perceived information yielded by scientific outlook, further delve into the deep penetralias of human mind. " So, is there a ground for religious outlook today?
- There is, and here's why. We are still unable to comprehend and explain a lot in the Universe. For example, many riddles are connected with the fundamental physical constants. Their values are just right to sustain the Universe. Should the value of the gravitation constant, the electron charge or the speed of light change but slightly, the world around us will collapse.
Who has set such values? This is a philosophic question. That's where the notions of the Creator and faith come in. What I do not accept, though, are primitive speculations on this account. We are still infants in the Universe and do not realize our role in it. How can we be sure that human mind has attained the absolute knowledge of the world infinite in time and space? Therefore, there is still room for religion-contemporary and civilized. But the further we expand the human comprehension of the Universe, the more will religion change. Just as science.
Illustrations supplied by the author
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