Humans have made enormous efforts to know what their habitat was like millions of years ago. It has given birth to both theories and apocryphal stories and even predicted doomsday scenarios. There were life and organisms, whose presences have been confirmed to some extent through evidence.
The answer to how it all began remains behind the clouds, like an evanescent sun on a rainy day. Studies have narrowed down to another aspect of the baffling challenge – What were the first life forms like?
In a paper published in the journal Proceedings of the National Academy of Sciences, scientists have considered an ancient electron transport chain (ETCs) to link early evolutionary history and a protocellular stage that came before it.
The study of early evolution and origin can be divided into two paradigms: bottom-up and top-down. Taking the bottom-up approach, successful experiments remain a validation of the proof of principle while top-down studies on early evolutionary history can provide a historical account of ancient organisms, but are unable to go into the stages that occurred during and just after the origin of life.
“The most basic features of biology, that organisms are made of cells, that they pass genetic information through DNA, that they use protein enzymes to run their metabolism, all emerged through specific processes in very early evolutionary history,” Aaron Goldman, Associate Professor of Biology at Oberlin College told phys.org.
Across all trees of life, adenosine triphosphate (ATP) synthase enzymes (a membrane-spanning multiprotein complex) have been observed, which are powered by proton or ion gradients and produced almost always by ETCs.The first ETC is mitochondria, try and recall biology lessons, where the ETC comprises four complexes, three of which act to pump protons across the membrane. Other than respiration, ETCs are used to conserve energy in photosynthesis.
The study suggests that certain components of ETCs date back to pre-Last Universal Common Ancestor (LUCA) while recent lab experiments on prebiotic chemistry and protocells have advanced allowing some steps in ETCs to be performed in simulated early Earth milieu without involving proteins. Researchers have posited that top-down and bottom-up methodologies can be combined to have a better understanding of the earliest evolution of membrane bioenergetics, getting close to comprehending the origin of life. The broad range of metabolic strategies recorded across the bacteria and archaea also brings a diverse array of energy-conserving ETCs, which have similarities and evolutionary relationships.
The study points out that phylogenetic (evolutionary development and diversification of species, and organisms) evidence reveals that the machinery for embedding proteins into membranes and transporting them across membranes was present before LUCA. Although it’s an inchoate research topic, experiments have shown that some elements of electron transfer chemistry, proton gradient generation, and phosphate bond formation, the basis of all modern ETCs, can be recreated without protein components. However, an ETC-like system cannot itself indicate that such a scenario existed during the origin of life, but peeling off the early evolutionary stages could shed light on how the primary ETCs evolved, when and the geochemical factors that propelled the evolutionary process.
This research has been bolstered by five years of earlier work by the team led by Laura M Barge at the Nasa Jet Propulsion Laboratory.