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How life arose remains a looming question in science that researchers are seeking to answer by studying the features shared among life today. Everything alive is made up of cells, and what made the first cells different from chemical reactions occurring in the environment is a membrane.

By investigating what properties these early membranes may have had, scientists can better understand how life began and evolved into the diversity of organisms we have today.

An important feature of membranes is what they allow to pass through and what they stop from entering the cell. This influences which molecules are involved in the biological processes that keep cells ticking.

The researchers focused on a few types of molecules essential for all life: the sugars that make up the backbone of DNA and RNA and the building blocks of proteins, known as amino acids. They were interested in these molecules not only because they are so pervasive across life, but they also twist in specific ways.

The work has been published in .

Biological molecules have a property called chirality, which refers to the way the molecule turns. It's like comparing your left hand to your right hand. Your hands are made up of the same structures, organized in fundamentally the same way, but flipped so that they are not identical.

In biology, chirality is important for how molecules interact. For example, all the sugars in DNA and RNA need to have the same chirality (all be right-handed) to assemble into the backbone of a DNA or RNA strand. However, why life chose one chirality over the other has remained a lingering question.

The researchers propose that early membranes may have played a key part in selecting the right-handed sugars and left-handed amino acids that all life uses today.

They analyzed what was able to pass through membranes with properties similar to those of archaea, a major group of microbes. The researchers also tested a membrane they designed that mixes archaeal and bacterial properties. For both types of membranes, the right-handed DNA and RNA sugars more easily passed through, while the left-handed versions had trouble permeating.

There was more variability among amino acids. Some left-handed amino acids were more likely to pass through the membrane with mixed bacterial and archaeal properties. This included the amino acid alanine, which is thought to be one of the first amino acids used by life.

While this study doesn't paint a complete picture of the amino acids our cells use today, these findings demonstrate how differences in membranes strongly affect which amino acids are able to pass through.

Since the membranes studied are only approximations of what the first life on Earth may have been encased in, there may be other, unknown properties of the earliest membranes that influenced what we now consider our most essential molecules.

The authors add, "All known life uses a specific stereochemistry: left-handed amino acids and right-handed DNA. Understanding how this evolved is a long-standing mystery key for understanding the origin of life. Our experiments show that a specific type of membrane鈥攖he structure that encloses cells鈥攁cts as a sieve that selects for the stereochemistry life uses."