The subtle movement of proteins helps modern cells to proliferate. During cell division, structural enzymes and proteins organize DNA replication and division of cell cytoplasmic contents and membrane division. Doing these processes correctly is very important; Because the error can lead to the production of abnormal daughter cells or the ability to survive.
Billions of years ago, the same challenge must have been faced by the first membrane assemblies that arose spontaneously from inanimate matter; But these protocols (precursors of living cells) had to be amplified without relying on large proteins. How they did this is an important question for astronomers, biologists and biochemists studying the origin of life. Anna Wang“If you remove all the cell enzymes, nothing will happen,” said an astronomer at the University of New South Wales in Australia. “They are very stable.”
In a recent study published in the Biophysical Journal, Roman Atal, Physicist of the City of Science and Technology of France and Lauren Schwartz From the public hospitals of Paris they developed mathematical equations that show how heat alone could have been sufficient to guide one of the most important parts of the replication process, the splitting of the protocol and its division.
Atal thinks that the chemically and physically active processes in early life were probably very simple; Thus, thermodynamics alone could have played an important role in how life began. According to him, the fundamental equations he worked on could explain some of the laws governing the primordial origin of life.
Flip to split
Stem cells will need a physical or chemical stimulus to divide without complex protein machinery. Discovering the processes that led to the division of the first cells becomes even more challenging when you consider that scientists have not yet agreed on the definition of life and protocols.
What scientists agree on is that protocols must have some kind of inherited information that can be passed on to daughter cells and have a metabolism that performs chemical reactions and has a lipid membrane that separates the inherited metabolism and information from their environment. . While the chemical world outside was random, the provided lipid membrane walling could create a region with less entropy.
In order for a protozoan to grow before division, it must not only increase the volume within the cell, but also the surface area of the surrounding membrane. Additional lipids for their membranes are needed to make two smaller daughter cells the same size as the parent cell; Because their surface will be larger compared to the volume.
As a result of the chemical reactions needed to provide the fuel needed to produce lipids, energy is released in the form of heat. As Atal shared these ideas with Schwartz, he wondered if this energy was enough to stimulate the initial division of the cell.
Atal, researching research papers, found a study that showed that mitochondria were slightly warmer than the cells around them. He wanted to know if this energy difference could be created in the protocols and if it was enough to start the division. Atal devised equations to model this problem. He hypothesized that protocols are rod-shaped and have a bilayer membrane that allows nutrients and waste to be released.
Atal found that the energy produced by the primary cellular metabolism heats up intra-membrane lipids faster than extra-membrane lipids. Then, the thermodynamics of the energetic inner lipids force them to rotate outward and expand the outer membrane. An easy solution to this imbalance is for the cells to press together to form two daughter cells. This compression occurs in the middle of the parent cell, which is the hottest spot and has the most lipid movement.
Atal’s work is purely theoretical; But it can be tested in the laboratory by making similar vesicles and measuring whether the temperature inside them is different from the temperature outside. Lack of asymmetry in lipid membranes could play a role in early life, Wang says. Although both he and Paul HiggsMcMaster University biophysicists are skeptical of some of Atal’s model hypotheses.
They noted that because cells and protocells are small, very little heat can be generated, and it is unclear whether the temperature difference is large enough to start the fission process before the heat spreads across the membrane.
Wang is also skeptical about the proposed movement of lipids between the inner membrane and the outer membrane. In today’s membranes, lipids are not easily displaced; Because their molecules have complex structures. Of course, this may not be the case with the simpler lipids used to create early life. He said that when such vesicles are produced in the laboratory, they move around irregularly and you can not stop them.
Higgs also refutes Atal’s assumption that cells are rod-shaped. This form requires special proteins to hold the membrane in place that the protocells lacked; As a result, they will be spherical, not rod-shaped. “I do not know how to maintain the shape of a bar without a hard wall,” he said.
None of this means that heat played a role in the initial cell division, Wang says; Rather, Atal’s mathematical model may not be the most accurate model possible. However, Claudia Bonfio“This article adds to the existing scientific work on early life,” says a biochemist at the University of Strasbourg in France. Because it is a good starting point for experiments. We often forget that reactions consume and produce heat, and this can affect things like fission.
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