Could the Chemoton Conquer RNA World?
One of the leading hypotheses for the origin of life is called 'RNA world'. In this model, self-replicating ribonucleic acids (RNA) proliferated in Earth's primordial soup and slowly but surely evolved into proteins, which evolved into DNA, which evolved into ever more complex life. Composed of sugars, phosphate groups, and nitrogenous bases, RNA molecules are essentially half-size DNA molecules. If RNA world is correct, they could also be Earth's first 'living' fossils.
Whether RNA world actually happened is far from certain, but the idea certainly has attracted lots of scientific attention since MIT biologist Alexander Rich first proposed it in 1962. Many thousands of papers have been published on it. Contrast this formidable scientific fame with that of another theory of life first put forward around the same time. The Chemoton hypothesis garners just 18 results in a cursory search of the scientific database PubMed, but a rising number of researchers are starting to insist that it merits much more attention.
The chemoton is an abstract model of what could be the fundamental unit of life. Here's the jargon-y definition, courtesy of UC-Davis philosopher of biology, James R. Griesemer:
A chemoton is any autocatalytic chemical super-system composed of three autocatalytic subsystems: (1) GEN: a genetic polymeric material (pV) comprised of monomers (V) undergoing (template) replication, (2) MET: a metabolic network of monomers (Ai) that plays an equilibrating role, running on the energetic difference between food input (Xi) and waste output (Yi), and (3) MEM: a membrane (Tm) comprised of components synthesized from products of the metabolic network (Tn) and the genetic cycle (R).
That wordy description can be distilled into something much more palatable without sacrficing accuracy: "genes, metabolism, and membrane," science writer Michael Marshall wrote for National Geographic. When metabolism and self-replication are wrapped in a lipid shell, the most basic life – the chemoton – has emerged.
Hungarian scientist Tibor Gánti conceived the chemoton as early as 1952 and formally described it in his book Az élet princípiuma in 1971. The book's title hints at why the chemoton has not received much attention. It was announced to the world in Hungarian, at a time when Hungary was behind the Soviet Union's Iron Curtain. The chemoton would not reach English readers until 2003, when RNA world was firmly entrenched as the leading theory of life's origins.
Where the chemoton and RNA world collide is on enzymes. While Gánti's theory views enzymes as the result of a long evolutionary process within cells, RNA world sees them as fundamental – RNA enzymes, called ribozymes, may have been performing all sorts of functions necessary to the proliferation of early RNA-based life.
For now, the conflict between the chemoton and RNA world is squarely academic, with RNA world far ahead in the evidentiary lead, but that could change if scientists start looking for signs of chemoton formation in laboratory settings.
“For scientists attempting to re-create the spark of life, the chemoton offers an attractive target for experiments,"Marshall wrote. "If non-living chemicals can be made to self-assemble into a chemoton, that reveals a pathway by which life could have formed from scratch. Even now, some research groups are edging startlingly close to this model."