PICTURE: Somewhere in a hostile environment in early soils, life was born.see more Credit: Not Available Our prehistoric land, bombed…
PICTURE: Somewhere in a hostile environment in early soils, life was born.
Credit: Not Available
Our prehistoric land, bombed with asteroids and lighting, with bubbling geothermal pools, may not be hospitable today. But somewhere in the chemical chaos of our early planet, life was formed. How? For decades, researchers have tried to create miniature replicas of babies in the lab. There they search for the main ingredients that created the essential building blocks for life.
It’s attractive to chase our story. But this endeavor can give more than just excitement. Knowledge of how the Earth built its first cells could inform our search for alien life. If we identify the ingredients and the environment required to spark spontaneous life, we could look for similar conditions on planets throughout our universe.
Today, much of the research’s origins focus on a specific building block: RNA. While some researchers believe that life was formed by simpler molecules and only later developed RNA, others see evidence to prove (or disprove) that RNA was formed first. A complex but versatile molecule, RNA stores and transmits genetic information and helps synthesize proteins, making it a competent candidate for the backbone of the first cells.
To verify this “RNA World Hypothesis”, researchers face two challenges. First, they must identify which ingredients reacted to create the four nucleotides of the RNA ̵
1; adenine, guanine, cytosine and uracil (A, G, C and U). Secondly, they must determine how RNA stored and copied genetic information to replicate.
So far, researchers have made significant progress in finding precursors to C and U. But A and G are still modest. Now, in a paper published in PNAS Jack W. Szostak, professor of chemistry and chemical biology at Harvard University, together with first author and doctoral student Seohyun (Chris) Kim suggested that RNA could have begun with another set of nucleotide bases . Instead of guanine, RNA could have invoked a surrogate – inosin.
“Our study suggests that the earliest forms of life (with A, U, C and I) may have arisen from a different set of nucleobases than those found in modern life (A, U, C and G), “said Kim. How did he and his team come to this conclusion? Lab attempts to produce A and G purine based nucleotides, produced for many unwanted side products. Recently, however, researchers discovered a way to make versions of adenosine and inosine-8-oxo-adenosine and 8-oxo-inosine – from materials available on the original soil. So, Kim and his colleagues decided to investigate whether the RNA constructed with these analogues could replicate effectively.
But substitutes failed to perform. Like a cake baked with honey instead of sugar, the final product may look and taste similar, but it does not work as well. The honey cookie is burning and dripping in liquid. 8-oxo-purine RNA still performs, but it loses both the speed and accuracy needed to copy. If it replicates too slowly, it falls apart before the process is completed. If it makes too many errors, it can not serve as a faithful tool for propagation and evolution.
Despite its inadequate performance, the 8-oxo-purines resulted in an unexpected surprise. As part of the test, the team compared 8-oxo-inosine’s ability to a control, inosin. Unlike its 8-oxo counterpart, the inosin enabled RNA to replicate at high speed and cause errors. It turns out to show reasonable prices and credibility in RNA copying reactions, concluded the team. “We suggest that inosin could have served as a surrogate for guanosine in the early stages of life.”
Szostak and Kim’s discovery could support the RNA world hypothesis. Over time, their work can confirm the primary role of RNA in our history. Or, researchers can find that early land offered several ways for life to grow. Finally, armed with this knowledge, researchers could identify other planets that have the essential ingredients and decide if we share this universe or are alone alone.