Evolution on a chip
All the more important is the result of Brian Pegel and Gerald Joyce from the Scripps Research Institute in California, who received practical confirmation of the supposedly speculative hypothesis.
They were able to realize the chemical evolution of RNA molecules in accordance with the principles of Darwinian theory. And although "intelligent design" (as the outwardly more civilized form of creationism is now called) is present in their experimental setup, the intervention of "higher intelligence" in its work is not required.
In the latest issue of the journal PLoS Biology, an article appeared describing an ornate biochemical experiment during which scientists were able to carry out the directed evolution of biological molecules (Brian M. Paegel, Gerald F. Joyce, Darwinian Evolution on a Chip).
Researchers have created an installation that is controlled by an autonomous computer and is able to direct the evolution of so-called RNA enzymes – catalysts of biological processes based on RNA – without human intervention.
The evolution of chemical molecules in a scientific experiment is not at all a discovery of scientists, although the catalytic activity of special types of RNA was discovered relatively recently (before that, scientists considered only the synthesis of proteins to be the sphere of activity of RNA). The first RNA enzymes of laboratory origin were obtained in the 90s of the last century.
The main achievement of scientists is the automation of the natural selection of biological molecules in accordance with their properties. The selection is carried out by a machine, and human intervention is required only at the stage of replenishment of consumable chemical reagents. Well, the toggle switch at the very beginning should be turned on by someone.
The automatic system of chemical evolution works according to the same principles as Darwin's theory of evolution.
The selection process begins with the fact that a set of slightly different RNA enzymes called RNA ligases is involved in the model catalysis reaction. In living organisms, RNA ligases combine two RNA molecules to form a phosphodiester bond. Those enzymes that catalyze this reaction automatically attach a so-called promoter RNA sequence to their molecule, its presence allows such RNA molecules to react with RNA polymerase.
As a result of the last interaction, the catalyst molecule is copied – in a sense, it has a "direct descendant".
Thus, the molecules of RNA enzymes that have successfully entered into the catalysis reaction are doubled, and the total number of successful molecules begins to prevail over the molecules less active in the reaction under consideration. It is here that scientists boldly draw an analogy between more hardy and tenacious animals that bring more offspring to the species compared to weak ones, as a result of which a positive mutation becomes common to the whole species.
In the process of replication, RNA enzymes underwent random mutations, just as cellular DNA and RNA undergo them in living systems. Such mutations can randomly change the catalytic activity of molecules both for the better and for the worse.
The automated evolutionary laboratory of scientists worked according to an iterative (step-by-step) principle: after the first cycle of catalysis of the reaction with the substrate, the development of an increased concentration of the most active ligases, the reaction stopped, and all the components of the mixture were thrown into a new reaction cell with a fresh substrate.
There, the catalysis reactions continued again until the substrate was developed, after which the substances were again transferred to a fresh reaction cell.
The driving force behind the evolution of molecules was a gradual reduction in the amount of substrate, which catalysts reacted with. These properties are similar to the property of variability of living systems, as well as the possibility of transmitting a new, mutated genome by inheritance. It is the limitation of the reaction substrate that acts as a factor of the pressure of natural selection.
As a result, after a 70-hour process during which the original RNA ligase molecules underwent billions of replications, scientists found that the most adapted catalysts were able to accelerate the reaction by 90 times compared to their initial catalytic activity.
Their increased activity was eventually determined by 11 mutations. The randomness of these mutations is the most illustrative example of the work of evolutionary theory. This means that by imposing an evolutionary load on some other molecules - for example, the limitations of the substrate or the need for selective interaction with a certain type of reagents, one can hope that in the end the evolved molecules will be more active in those types of reactions where it is necessary.
However, it is impossible to predict the nature of mutations that cause the advantages of new molecules, their type and quantity.
Two completely identical experiments can lead to molecules similar in properties, but completely different in structure.
The development of scientists can find application in the creation of new highly sensitive biological sensors, the creation of new catalysts or the production of molecules with completely new properties. In addition, it is difficult to overestimate the educational significance of such systems: now students and schoolchildren and everyone can see the evolutionary theory in action with their own eyes.
At the same time, the creators of the system recognize that the evolution of molecules and the evolution of living systems are completely different processes in complexity and their result can only serve as a visual demonstration of the validity of Darwin's provisions, but not a confirmation of its work in the real world.
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09.04.2008