Scientists are still grappling with the mystery of how life on Earth began, with one key focus being the properties that define all living organisms. Central to this investigation is the presence of cells, particularly the membrane that separates the cell’s contents from the external environment, distinguishing life from mere chemical reactions.
To shed light on the origins of life and the evolution of modern organisms, researchers are delving into the characteristics of the very first cell membranes. Of particular interest is which substances can pass through the membrane and which are blocked, as this directly influences the molecules involved in biological processes.
One vital aspect that researchers are examining is the chiral nature of essential molecules like sugars, which form the backbone of DNA and RNA, as well as amino acids, the building blocks of proteins. These molecules exhibit chirality, meaning they have a distinct left or right-handed orientation which is crucial for the functioning of living organisms.
Recent research, published in PLOS BIOLOGY, explores the possible reasons behind the selection of specific chiralities in ancient cell membranes. Scientists studied how different sugars and amino acids passed through membranes resembling those of ancient archaea, a group of microorganisms, as well as a hybrid membrane combining characteristics of both archaea and bacteria. They found that “right-handed” sugars crucial for DNA and RNA synthesis passed through these membranes more easily, while “left-handed” forms were impeded.
The passage of amino acids through these membranes was more complex, with some “left-handed” amino acids, such as Alanine, a primitive amino acid present in the early stages of life, able to traverse the hybrid membrane.
While the study’s results do not provide a definitive answer as to why modern cells utilize specific amino acids, they do highlight the significant impact of membrane properties on the molecules essential for life. The researchers emphasize that the ancient membranes studied are simplified models, and the first cells may have had additional unknown features that influenced molecular selection.
Nevertheless, the study’s findings suggest that the cell membrane may have acted as a sieve, favoring certain molecules at the dawn of life, ultimately shaping the fundamental building blocks of life as we know it today.