Cells are defined by their membranes, which regulate what substances can enter or leave. This control is especially relevant to key molecules like the sugar components of DNA and RNA and the amino acids that form proteins. These molecules share an important feature: chirality, or handedness. In biology, all DNA and RNA sugars are right-handed, while amino acids are left-handed. The reason for this consistent stereochemistry has remained an open question in origin-of-life research.

Researchers from the University of Oxford and collaborating institutions studied how membranes with properties similar to those found in archaea-one of the earliest forms of life-allowed various chiral molecules to pass through. They also designed a synthetic membrane combining traits of both archaeal and bacterial membranes. Both types of membranes more readily permitted the right-handed forms of DNA and RNA sugars to pass, while left-handed variants were restricted.

The findings for amino acids were more nuanced. The mixed-type membranes allowed some left-handed amino acids, like alanine, to pass through more easily. Alanine is hypothesized to be one of the first amino acids utilized by primitive life. While these membranes do not replicate the exact conditions of Earth's earliest cells, they offer insight into how molecular selection may have occurred.

The authors stated, "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 - the structure that encloses cells - acts as a sieve that selects for the stereochemistry life uses."

Early membranes may have been instrumental in establishing the biochemical asymmetry observed across all life today, acting as selective barriers that helped shape the molecular foundations of biology.