How to create a molecular machine without the help of a living cell?
"Wildlife – the world of molecular machines"
ru"" gave a lecture on "Molecular machines: what are they and how to make them?".
All processes in living cells are carried out by structures that can be called molecular machines, or "nano-machines". Hemoglobin delivers oxygen to the cell, ATP is synthesized in the mitochondria, and substances are constantly transported through the cell membrane, both inside and out. RNA is built on the basis of a DNA molecule, and proteins are synthesized in ribosomes based on RNA. In general, the cage resembles a conveyor belt or even a whole factory with many units working continuously and accurately. At the same time, the objects that are processed on the "machines" of this plant are individual molecules and atoms.
But not only is the combination of amazing precision and small size unusual in this "factory". It must be remembered that this plant assembled itself and maintains its own functioning. After all, all "molecular machines" are assembled according to instructions written in DNA, and DNA and RNA molecules are assembled by molecular machines. Thus, as V. A. Avetisov formulated: "A cell is an operating system built of molecular machines and producing molecular machines."
Another equally striking property of molecular machines is due to the fact that fluctuations are very strongly manifested at the atomic level. The fluctuations of the atom reach 1 angstrom, whereas the protein molecule must move this atom to the right place with an accuracy of 0.1 angstrom. If the atoms do not take exactly the right position, the biochemical reaction carried out by our molecular machine simply will not happen. V. A. Avetisov compared this to an attempt with shaking hands to get a thread into the eye of a needle.
The principle by which molecular machines operate does not differ from the principle that exists in "big" mechanics: "to work accurately, you need to work slowly." The lecture demonstrated the study of how the myosin protein molecule, which forms contractile muscle fibers, behaves. It is a complex molecule consisting of many atoms. The proper motions of the parts of the molecule were studied. Simplistically, it can be represented in the form of atoms interconnected by elastic bonds. If this construction is set in motion, then the atoms can oscillate relative to each other in a variety of ways: the system has a lot of degrees of freedom.
In fact, it turns out that the myosin molecule, excited when receiving energy, will indeed experience rapid random fluctuations of its various parts, but very quickly these fluctuations are reduced to slower movements of its large subunits, and other fluctuations of parts of the molecule are gradually becoming rarer and rarer. In other words, a molecular machine turns out to be able to transform perturbations of fast degrees of freedom into mechanical movements of one or two large subunits. Here V. A. Avetisov gives an analogy with a piston in a steam engine, which performs relatively slow mechanical movements under the influence of fast and random movements of molecules.
Can we artificially create such a nano-machine capable, despite multiple fluctuations, of accurately working with atomic-scale objects? For example, to make an artificial nano-incinerator, that is, a molecular structure that converts thermal energy into mechanical motion. Of course, molecular machines are created by genetic engineering methods, when people change the instructions written in DNA and force the cell to synthesize certain proteins. But scientists want to learn how to create molecular machines that are fundamentally different from those that work in a living cell, which cannot be created by encoding the desired protein in DNA. How to create a molecular machine without resorting to the help of a living cell?
Polymers can be used for this, but not all kinds. The fact is that important properties of molecular machines are provided by their structure. If we take just a polymer globule resembling a myoglobin globule, we will find that the structure of its own oscillations is not the same as that of a protein: fast chaotic oscillations do not fade, being reduced to one or two slow movements of large parts of the molecule, but continue for a long time and without any order. That is, an ordinary polymer globule is not suitable for the role of a molecular machine at all.
Another thing is a fractal globule. In it, the protein thread is not wound into a chaotic tangle, but is laid fractally, that is, its bends are reproduced similarly at a higher level. In other words, it has the property of self-similarity. This method of laying strands of protein molecules was previously described in a lecture by Polit.ru Doctor of Physical and Mathematical Sciences Sergey Nechaev. So it turns out that the fractal structure just allows you to transfer energy from fast degrees of freedom to slow ones. And the behavior of a fractal globule under energetic excitation is the same as that of a natural protein molecule. This means that hierarchy and self–similarity are what is needed to create artificial molecular machines.
Portal "Eternal youth" http://vechnayamolodost.ru20.11.2013