快猫短视频

Cell-like structures containing very simple proteins and even pores in the membrane around them have been created in lab experiments that aimed to mimic the conditions found in the crust of early Earth.

鈥淲e start with very primitive chemicals, and we obtain something with increasing complexity and increasing order,鈥� says at the University of Duisburg-Essen in Germany. 鈥淲e believe that this system is very interesting to look at when it comes to the origin of life.鈥�

The experiment鈥檚 starting chemicals include simple fatty substances and amino acids 鈥� the building blocks of proteins 鈥� thought to have been present in the crust of early Earth. Such chemicals have been found inside 4-billion-year-old quartz rocks, says Mayer.

He and his colleagues put these chemicals in a container of water with carbon dioxide gas at a pressure of about 72 bar, the kind of conditions that might have been found in cracks and faults around a kilometre deep in the crust.

The team then varied the pressure slightly thousands of times. This kind of pressure cycling can occur naturally in geyser systems and may have occurred on early Earth due to tidal forces, says Mayer.

鈥淭he moon was much closer to Earth during that period, and the tidal influence was much stronger,鈥� says Mayer, who recently presented the team鈥檚 findings at a meeting of the European Geosciences Union in Vienna, Austria.

When the pressure goes up, it makes the CO₂ become what is known as a supercritical fluid, letting it dissolve fatty substances. When the pressure goes down, the fatty substances that have a water-attracting part as well as a water-repelling oily part spontaneously form cell-like spheres, or vesicles, with bilayer membranes similar to those found in living cells.

Some of the amino acids also join together to form simple proteins called peptides. So far, the team has found peptides up to eight amino acids long.

The vesicles and peptides usually break up during the next pressure cycle. But sometimes peptides with water-repelling properties get incorporated into the membrane. This protects the peptides, which then accumulate over cycles.

A few of these incorporated peptides straddle the membrane and stabilise it, allowing some vesicles to survive for several pressure cycles.

One peptide found in recent experiments can even clump together in groups of six to form pores in the membrane through which water and ions can flow. This can reduce pressure differences and prevent the vesicles from bursting.

This shows there is a selection for specific peptides and another for more stable vesicles, says Mayer. 鈥淭hese two selection processes interact in a way that means the system becomes more and more complex, and more and more functional. We find that pretty exciting.鈥�

What鈥檚 more, the flow of chemicals through the pores is a potential source of energy. All living cells derive their energy from ions flowing through pores in membranes, says Mayer.

It is widely thought that life began with RNA molecules that were capable of acting as enzymes and of replicating themselves, a stage known as the RNA world. 鈥淭hese vesicles could have been the ideal environment where the RNA world could have started,鈥� says Mayer.

鈥淚 find the work very interesting and certainly important,鈥� says at the University of Bern in Switzerland, who chaired the session in which Mayer presented his findings. But it is unclear how relevant the research is to the origin of life, because we can鈥檛 be sure if the experiments reflect the chemicals and conditions present on early Earth, she says.