Calcium may have unlocked the origins of life's molecular asymmetry

Summary

A new study led by researchers at the Earth-Life Science Institute (ELSI) at Institute of Science Tokyo has uncovered a surprising role for calcium in shaping life's earliest molecular structures. Their findings suggest that calcium ions can selectively influence how primitive polymers form, shedding light on a long-standing mystery: how life's molecules came to prefer a single "handedness" (chirality). Like our left and right hands, many molecules exist in two mirror-image forms. Yet life on Earth has a striking preference: DNA's sugars are right-handed, while proteins are built from left-handed amino acids. This phenomenon, called homochirality, is essential for life as we know it -- but how it first emerged remains a major puzzle in origins of life research. The team investigated tartaric acid (TA), a simple molecule with two chiral centers, to explore how early Earth's environment might have influenced the formation of homochiral polymers. They discovered that calcium dramatically alters how TA molecules link together. Without calcium, pure left- or right-handed TA readily polymerises into polyesters, but mixtures containing equal amounts of both forms fail to form polymers readily. However, in the presence of calcium, this pattern reverses -- calcium slows down the polymerisation of pure TA while enabling mixed solutions to polymerise. "This suggests that calcium availability could have created environments on early Earth where homochiral polymers were favoured or disfavoured," says Chen Chen, Special Postdoctoral Researcher at RIKEN Center for Sustainable Resource Science (CSRS), who co-led the study. The researchers propose that calcium drives this effect through two mechanisms: first, by binding with TA to form calcium tartrate crystals, which selectively remove equal amounts of both left- and right-handed molecules from the solution; and second, by altering the polymerisation chemistry of the remaining TA molecules. This process could have amplified small i...