The book "Life on the Edge. Your first book on quantum biology. ”

Life is the most extraordinary phenomenon in the observable universe; but how did life come about? Even in the era of cloning and synthetic biology, a remarkable truth remains valid: no one has yet managed to create life from completely non-living materials. Life arises only from life. It turns out that we still miss one of its fundamental components?

Like Richard Dawkins’s book The Selfish Gene, which made it possible to take a fresh look at the evolutionary process, the book Life on the Edge changes our understanding of the fundamental driving forces of this world. In it, the authors consider both the latest experimental data and discoveries from the forefront of science, and they do this in a uniquely intelligible style. Jim Al-Khalili and Jonjo McFadden talk about the missing component of quantum mechanics; the phenomenon that underlies this most mysterious of sciences.

Kinetic isotope effect

Have you ever tried to ride a bike to the top of a hill? If you tried, then you probably overtook pedestrians. On a flat road, driving a bicycle, you would easily overtake all pedestrians and even runners. So why is cycling on a hillside less productive?

Now imagine that you got off your bike and walked on foot, driving it along a flat road or along a hillside. Now everything is obvious. Walking along the slope, you not only have to climb yourself, but also push up the bike. The weight of the bike, which did not have much importance when driving on a horizontal surface, is now working against you when you are trying to climb the top of a hill: you are pulling a bike on yourself, over many meters overcoming the force of gravity of the Earth. This is why racing bike manufacturers attach great importance to how easy a bike model will be. Of course, the weight of an object is of great importance in the event that a person has to move it, however, our example with a bicycle rather indicates that not only the weight of the object to be pushed is important, but also the type of movement.
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And now imagine that you want to know what is between two cities, say A and B, lies the terrain: flat or hilly. At the same time you did not have the opportunity to go to these cities and check it personally. If you know that there is a mail service between these cities, and the postmen use light and heavy bicycles, one of the options to find out the relief features is this: you need to send sets of the same parcels from one city to another, with half of the parcels being sent with postmen on light bicycles, and the second with postmen on heavy ones. If it turns out that the delivery of all your parcels took approximately the same time, you can conclude that the terrain between cities is more likely flat. If the delivery of parcels on heavy bicycles took much longer, you will realize that the terrain between A and B is rather hilly. Thus, our postmen-cyclists are engaged in sounding unexplored territories.

Atoms of any chemical element are, like bikes, of different weights. Take, for example, hydrogen - the simplest element, which nonetheless is of great interest to us. Each element is determined by the number of protons in the nucleus, which coincides with the number of electrons surrounding the nucleus. So, in the hydrogen nucleus there is one proton, in the helium nucleus - two, lithium - three, etc. However, the atomic nuclei contain not only protons, but also neutrons, which we mentioned in Chapter 1, when they spoke about the fusion of hydrogen nuclei inside The sun If neutrons enter the nucleus, it becomes heavier and its physical properties change. Atoms of one element differing in the number of neutrons in the nucleus are called isotopes. The usual isotope of hydrogen is the lightest, since it consists of only one proton and an electron. This is the most common form of hydrogen. There are two more rare isotopes of hydrogen: deuterium (D), which has one extra electron, and tritium (T), which has two extra neutrons.

Since the chemical properties of elements are mainly determined by the number of electrons in the atoms, different isotopes of the same element, differing in the number of neutrons in atomic nuclei, will have very similar, but not identical, chemical properties. The kinetic isotope effect shows how sensitive a chemical reaction is to replacing atoms in the molecule of a reacting substance with heavier isotopes. It is defined as the ratio of reaction rates occurring with heavy and light isotopes. For example, if water is involved in the reaction, then the hydrogen atoms in the H2O molecules can be replaced by their heavier counterparts, deuterium and tritium, forming the D2O or T2O molecules, respectively. Just like our postmen on bicycles, a reaction may react to a change in the weight of atoms, or it may not respond - it all depends on the way substances choose to react in order to eventually become its products.

There are several mechanisms that provide strong kinetic isotope effects. One of these mechanisms is quantum tunneling - a process that, like cycling, depends on the mass of the particle trying to overcome the barrier. The greater the particle mass, the less its wave properties manifest, and therefore, the lower the probability that the particle will overcome the energy barrier. Therefore, doubling the mass of an atom, for example, in the case of the replacement of the usual isotope of hydrogen by deuterium, sharply reduces the probability of its participation in quantum tunneling.

Thus, the presence of a strong kinetic isotope effect may indicate that the reaction mechanism — the path from reactants to products — implies quantum tunneling. However, this is not the only possible conclusion, since the effect may be due to classical chemical phenomena that are not related to the laws of quantum mechanics. But if quantum tunneling takes place during the reaction, the reaction should react in a certain way to the temperature change: its rate ceases to be accelerated and evened out at low temperature, as DeVolt and Chance showed in the case of electron tunneling. The same showed experiments Klinman and her team for the enzyme ADH, and in the course of the experiments were obtained strong evidence that quantum tunneling was in this case part of the reaction mechanism.

A team of scientists led by Klinman managed to obtain important evidence that proton tunneling often occurs during enzymatic reactions at temperatures at which life processes also take place. Other groups of scientists, including a group led by Nigel Skrapton of the University of Manchester, conducted similar experiments with other enzymes and observed kinetic isotope effects indicating that the reaction is accompanied by quantum tunneling. And yet, the question of how enzymes support quantum coherence and contribute to the emergence of the tunnel effect remains controversial. For some time it was believed that the enzymes are not static, that during the reactions they constantly oscillate, move. For example, collagenase "jaws" open and slam each time they break a collagen bond. Scientists believed that such movements, observed during the reaction, are random or are designed to capture substrates and align and order all the atoms that react. However, in our time, experts in the field of quantum biology argue that such oscillations — the so-called “drive engines” and their main function — bring atoms and molecules together so that the quantum tunneling of particles (electrons and protons) is possible. We will return to this topic, one of the most fascinating and rapidly developing in quantum biology, in the last chapter of our book.

So what constitutes the “quantum part” of quantum biology

Every single biomolecule that exists or has ever existed in any living cell has been created and destroyed by enzymes. Enzymes, like no other substance, are close to the concept of the “driving forces of life”. The discovery that some (and possibly all) enzymes function on the basis of dematerialization of particles in one place of space and their instantaneous materialization at another point allows us to take a fresh look at the riddle of life. Despite the fact that many issues related to the functioning of enzymes are not fully understood (for example, the role of protein movement), there is no doubt that quantum tunneling plays a large role in the mechanism of their work.

Despite this, we cannot but take into account the criticisms expressed by many scientists. They recognize the discoveries of Klinman, Skratton and other researchers, but claim that quantum effects play the same role in biology as in the work of steam locomotives: they can be observed, but in general they do not contribute to understanding how the whole system functions. This argument often sounds in the debate about whether enzymes have learned to benefit from quantum phenomena like tunneling in the course of evolution or not. Critics argue that the emergence of quantum phenomena in the course of biological processes is inevitable due to the fact that most biochemical reactions simply occur at the atomic level. Quantum tunneling is not magic at all; This phenomenon occurs in our Universe since its inception. Of course, that which is the result of the “ingenuity” of life cannot be the focus. Nevertheless, we are inclined to believe that the appearance of a tunnel effect against the background of enzyme activity is not inevitable, given the conditions of the intracellular environment - the very high temperatures, humidity and chaotic crush of molecules.

As you remember, the living cell space is characterized by cramped. The cell is literally packed with complex molecules that are continuously in a state of excitement and turbulence, namely in a state of random motion. Recall the molecules are similar to the billiard balls scattering in different directions and repelling each other (we talked about this in the previous section due to the fact that the locomotive makes it go up the hill). As you remember, it is this chaotic movement of particles that disperses and destroys fragile quantum coherence, so that the world we are used to seems “normal” to us. Scientists did not expect that quantum coherence can be maintained during molecular turbulence, so observing such quantum effects as tunneling in a stormy sea of ​​a living cell was an amazing discovery. Some ten or more years ago, most scientists abandoned the idea that tunneling and other unstable quantum phenomena can be observed in biological processes. The fact that these phenomena were found in biological environments suggests that life takes special measures to get the most out of the quantum world and keep its cells working . But what kind of action does life take? How does the way of life manage to keep the main enemy of quantum particle behavior - decoherence - at a distance? This is one of the greatest mysteries of quantum biology, to the clue of which scientists are gradually moving. We will talk about this in the last chapter of our book.

But before starting a new topic of our conversation, let's return to the place where we left our nano-submarine, namely, the active center of the enzyme collagenase inside the endangered tail of the tadpole. We quickly leave the active center, as soon as the "jaws" of the enzyme open, releasing the collagen chain (and you and me). We say goodbye to a mollusk-like enzyme molecule that goes to the next peptide bond in the chain to destroy it. Then we make a short trip through the body of a tadpole and observe the usual work of some other enzymes, which is just as important for the vital activity of the body as the work of collagenase. Following the cells leaving the tail of the tadpole disappearing before our eyes and heading towards the developing hind limbs, we observe the emergence of new collagen fibers that are laid like new railway tracks to accelerate the formation of the body of an adult frog. Often they arise from the very cells of the disappearing tail. New fibers are formed by enzymes that capture the blocks of amino acids released by collagenase and weave them into new collagen fibers. We do not have time to immerse ourselves in these enzymes, but it is worth saying that in their active centers we would observe the same carefully set dance as in collagenase, only with the reverse sequence of movements. Biomolecules on which life depends - be it fats, DNA, amino acids, proteins, sugars - are formed and destroyed by various enzymes. In addition, any action that a young frog performs is due to the activity of the enzymes. For example, when an animal notices a fly, electrical impulses are transmitted from the eyes to the brain through special neurotransmitter enzymes contained in the nerve cells. When a frog throws out its long tongue, its muscle contractions, due to which the frog catches a fly and pulls the prey in its mouth, are controlled by another enzyme, myosin, contained in muscle cells. When a fly enters the frog's stomach, a whole group of enzymes accelerating the digestion and absorption of nutrients comes into play. Other enzymes are responsible for transforming these nutrients into body tissues. The enzymes of the respiratory chain, which are contained in mitochondria, help transform nutrients into the necessary energy for the body.

Any stage of the life activity of frogs and all other living organisms, any process that supports them and our life with you, is supported and accelerated by enzymes - the real engines of life. Their catalytic properties are due to the ability of some elementary particles to perform perfected choreographic numbers, and therefore, to come into contact with the quantum world and use its strange laws for vital purposes.

However, the tunneling of particles is far from the only phenomenon of the quantum world from which life draws benefits for itself. In the next chapter we will talk about the fact that one more mysterious phenomenon of the quantum world is involved in the most important chemical reaction of the biosphere.

More information about the book can be found on the publisher's website.
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