Every living being on this planet today traces its lineage back to a single common ancestor that existed approximately four billion years ago. Scientists refer to this entity as the “Last Universal Common Ancestor” (LUCA).
Evidence suggests that many characteristics observed in contemporary organisms were already features of our ancient, shared forebear: cells possessed membranes, and genetic coding was stored in DNA.
Given that these fundamental traits were already established, researchers aiming to decipher the genesis of life on Earth have delved even further into the past, focusing on evolutionary events that preceded LUCA’s existence.
A team of researchers from the United States, whose findings were detailed in the journal Cell Genomics, concentrated their efforts on a specific class of genes termed universal paralogs. These genes retain molecular memory of biological changes dating back prior to LUCA, placing them significantly older than the ancestor itself.
What Are Paralogs?
Paralogs constitute a set of related genes that have arisen through duplication events within a single genome, resulting in multiple copies. Humans offer a clear illustration of such duplication: our DNA harbors eight distinct hemoglobin genes, all responsible for generating proteins that transport oxygen throughout the bloodstream.
All these genes originated from a single ancestral gene present around 800 million years ago. Over extended timescales, recurrent errors during DNA copying led to the proliferation of additional gene versions, with each duplicate gradually evolving a specialized function.
Universal paralogs are exceptionally rare. These gene families exist in at least two copies within the genomes of nearly all life forms. Their widespread presence strongly indicates that the initial gene duplication event occurred before the emergence of LUCA. Subsequently, these duplicated genes were passed down through successive generations and persist in extant organisms today.
According to the researchers, universal paralogs hold substantial clues regarding the state of life preceding LUCA. By examining all known universal paralogs, the scientists determined that every one of these genes is involved either in protein synthesis or in the movement of molecules across cellular boundaries. This discovery implies that the fundamental processes of protein production and membrane transport were among the earliest biological functions to undergo evolutionary refinement.
Furthermore, the investigators studied a family of universal paralogs associated with integrating enzymes and other proteins into cellular membranes. The team successfully reconstructed the protein encoded by the original ancestral gene in this family.
This ancient protein, simpler than its modern counterparts, was nevertheless capable of anchoring to cell membranes and interacting with the machinery responsible for protein creation. It is hypothesized that this ancient protein aided early polypeptides in embedding themselves within primitive membranes, thereby offering insight into the operational mechanics of the very first cells.
The researchers anticipate utilizing artificial intelligence to identify novel families of universal paralogs and conduct deeper analyses of their ancient progenitors. This approach should yield a clearer evolutionary snapshot from before LUCA, shedding light on the very first appearance of life on Earth as we currently understand it.
Skeptics often liken the spontaneous generation of life on Earth to a hurricane sweeping over a junkyard and assembling a Boeing jet from the debris. However, our counterpoint is that the improbable only appears so due to a gap in our current comprehension.
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