Ever since the late 19th and century, physicists have known about the counter-intuitive property of some electrical circuits called negative resistance. Usually, increasing the voltage in a circuit leads to an increase in electrical current. But under some conditions, increasing the voltage can cause a decrease in current instead. This basically means that pushing harder on electric charges actually slows them down.
Due to the relationship between current, voltage and resistance, in these situations, the resistance produces power, not consumes it, which results in "negative resistance". Today, negative-resistance devices have a wide variety of applications, such as in fluorescent lights and Gan diodes, which are used in radar guns and automatic doors, among other devices.
The most well-known examples of negative resilience occur in the design of human devices, not in nature. However, in a new study published in New Journal of Physics Gianmaria Falasco and co-authors at the University of Luxembourg showed that a similar property called negative differential response is in fact a widespread phenomenon that occurs in many biochemicals reactions that occur in living organisms. They identify the property in several vital biochemical processes such as enzymatic activity, DNA replication and ATP production. It seems that nature has used this property to optimize these processes and make living things work more efficiently on a molecular scale.
"This anti-intuitive but still common phenomenon has been discovered in a wealth of physical systems since its first detection in low-temperature semiconductors," the researchers wrote in their paper. "We have shown that the negative differential response is a widespread phenomenon in chemistry with major implications for the efficiency of biological and artificial processes."
As the researchers explained, a negative differential response can occur in biochemical systems that are in contact with multiple biochemical reservoirs. Each tank tries to draw the system to a different equilibrium point (as a balance point) so that the system is constantly exposed to competing thermodynamic forces.
When a system is in equilibrium with its environment, any small disturbance or noise affecting the tanks usually causes an increase in the production rate of a product in accordance with positive entropy. The production rate of a product can be thought of as a chemical current. From this point of view, the increase in noise that causes an increase in chemical current is analogous to the "normal" case in circuits in which an increase in voltage causes an increase in electric current.
But when a system in contact with multiple tanks is out of balance, it may respond differently to noise. In a non-equilibrium system, additional factors play, so increasing the noise reduces the chemical current. This negative differential response is analogous to the case where electrical circuits exhibit negative resistance
In their work, researchers have identified several biological processes that have negative differential reactions. One example is substrate inhibition, which is a process used by enzymes to regulate their ability to catalyze chemical reactions. When a single substrate molecule binds to an enzyme, the resulting enzyme-substrate complex breaks down into a product, generating chemical current. On the other hand, when the substrate concentration is high, two substrate molecules can bind to the enzyme and this double binding prevents the enzyme from producing more product. Since increasing the concentration of the substrate molecule causes a decrease in the chemical current, this is a negative differential response.
As a second example, researchers have shown that a negative differential response also occurs in autocatalytic reactions – "self-catalyzing" reactions or reactions that produce products that catalyze the reaction itself. Autocatalytic reactions occur throughout the body, such as in DNA replication and ATP production during glycolysis. Researchers have shown that negative differential reactions can occur when two autocatalytic reactions occur simultaneously in the presence of two different chemical concentrations (reservoirs) in an out-of-equilibrium system.
Researchers also identify negative differential reactions in dissipative self-assembly, a process that requires energy to allow the system to self-assemble, which makes it far from equilibrium. Dissipative self-assembly occurs, for example, in the ATP-driven actin self-assembly, long thin microstructures in the cytoplasm of cells that give their cells a structure.
Nature does everything for a reason, and the presence of a negative differential response in living organisms is no exception. Researchers have shown that this property gives advantages to biochemical processes mainly in terms of energy efficiency. For example, inhibition of the substrate allows the system to reach homeostasis with less energy than would otherwise be required. In dissipative self-assembly, the negative differential response allows the system to realize an almost optimal signal-to-noise ratio, which ultimately increases the efficiency of the self-assembly process.
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Gianmaria Falasco et al. "Negative differential response in chemical reactions." A New Journal of Physics . Doi: 10.1088 / 1367-2630 / ab28be
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Anti-intuitive physical property found to be widespread in living organisms (2019, August 13)
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