At the dawn of life, the heat may have triggered cell division


Elegant ballet protein allows modern cells to replicate. During cell division, structural proteins and enzymes coordinate DNA replication, cell cytoplasmic content division, and cell-cleaving membrane fusion. The correctness of these processes is crucial because mistakes can lead to daughter cells that are abnormal or unsustainable.

Billions of years ago, the first self-organizing membrane bundles of chemicals that spontaneously formed from inanimate materials had to face the same challenge. But these protocells almost certainly had to replicate without relying on large proteins. How they did this is a key question for astrobiologists and biochemists studying the origins of life.

“If you delete all the enzymes in the cell, nothing will happen. “It’s just inert bags,” he said Anna Wang |, an astrobiologist at the University of New South Wales in Sydney. “They’re really stable, and that’s the point.”

However, in recent work in Biophysical Journal, Romain Attal, a physicist from the City of Science and Industry in France, and cancer biologist Laurent Schwartz of the Paris Public Hospitals developed a series of mathematical equations that model how heat alone could be enough to trigger an important part of the replication process: splitting one protocell into two .

Attal believes that the chemical and physical processes active in early life were probably quite simple and that only thermodynamics could play a significant role in how life began. He said that the types of basic equations he worked on could explain some of the rules that regulated how life first came into being.

“Temperature gradients are important for life,” Attal said. “If you understand the subject, you must be able to write down its principles.”

Flipping for Fission

In order for primitive cells to divide without complex protein machinery, the process would require a physical or chemical driver. “In fact, it’s about reducing the cell to its basic functions and thinking, ‘What are the basic physical and chemical principles, and how can we mimic that without protein?'” Wang said.

Discovering these processes becomes more challenging when you consider that scientists still cannot agree on a definition of life in general, and protocells in particular.

What scientists agree on is that protocells must have had some kind of hereditary information that they could pass on to daughter cells, a metabolism that performed chemical reactions, and a lipid membrane that isolates metabolism and hereditary information from random ones on the rest of the planet. primordial soup. While the external chemical world was inherently random, the division provided by the lipid membrane could create an area of ​​lower entropy.

In order for a protocell to grow before it divides, it would have to increase not only the volume inside the cell but also the surface area of ​​the surrounding membrane. In order to create two smaller daughter cells with the same total volume as the parent cell, additional lipids would be needed for their membranes, because their surface area would be larger in relation to their volume. The chemical reactions needed to start the synthesis of these lipids would provide energy in the form of heat.

As Attal discussed these ideas with Schwartz, he began to wonder if that energy was enough to trigger early cell division. A search of the research literature revealed that mitochondria (the energy center of the cell, which began as a symbiotic bacterium billions of years ago) have a slightly higher temperature than the surrounding cell. Attal wanted to know if this difference in energy could be created in protocells and if it was adequate to trigger fission.



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