LUCA:Last Universal Common Ancestor

In trying to find the elements necessary for the origin of life, another question of importance is "what was the last universal original ancestor of life?"

A 3.8-billion-year-old organism was not the creature usually imagined. In LUCA, the prevailing belief is that it was a heat-loving or hyperthermophilic organism; like those odd organisms living in the hot vents along the continental ridges deep in the oceans today, above 90 degrees Celsius .
However, the new data suggests that LUCA was actually sensitive to warmer temperatures and lived in a climate below 50 degrees.

The research compared genetic information from modern organisms to characterize the ancient ancestor of all life on earth. Researchers identified common genetic traits between animals, plant, bacteria, and used them to create a tree of life with branches representing separate species. These all stemmed from the same trunk – LUCA, the genetic makeup that we then further characterized.

The RNA Connection to the Origin of Life
What this means is that in the origin of life question an important step has taken place towards reconciling conflicting ideas about LUCA. In particular, they are much more compatible with the theory of an early RNA world, where early life on Earth was composed of ribonucleic acid (RNA), rather than deoxyribonucleic acid (DNA).

RNA is particularly sensitive to heat and is unlikely to be stable in the hot temperatures of the early Earth. But the data indicate that LUCA found a cooler micro-climate to develop, which helps resolve this paradox and shows that environmental micro domains played a critical role in the development of life on Earth.

RNA and the Origin of Life

What were the conditions necessary for the formation of life? Some scientists believe that RNA was responsible for the development. RNA, the single-stranded precursor to DNA, normally expands one nucleic base at a time, growing sequentially like a linked chain. The problem is that in the primordial world RNA molecules didn't have enzymes to catalyze this reaction, and while RNA growth can proceed naturally, the rate would be so slow the RNA could never get more than a few pieces long (for as nucleic bases attach to one end, they can also drop off the other).

The RNA mechanism to overcome this thermodynamic barrier has been studied by incubating short RNA fragments in water of different temperatures and pH. Under an acidic environment and temperature lower than 70 degrees Celsius, the RNA pieces ranging from 10-24 in length could naturally fuse into larger fragments. This was generally accomplished within 14 hours.

The operation involved the RNA fragments which came together as double-stranded structures then joined at the ends. The fragments did not have to be the same size, but the efficiency of the reactions was dependent on fragment size in which case the larger the better until an optimal efficiency is reached around 100 and then it drops again.

The researchers note that this spontaneous fusing, or ligation, would a simple way for RNA to overcome initial barriers to growth and reach a biologically important size; at around 100 bases long, RNA molecules can begin to fold into functional, 3D shapes.