Probably the biggest mystery of life is life itself. How did it start, and what were the events that led to such substantial human organizations that we see today? Researchers have found a new concept that differs from the classic one. It is possible that the DNA’s distant cousin, RNA, wears more hats than just being a messenger.
There are chances that life’s first spark came from a single strand of RNA molecule, the simplest self-replicating structure that later gave rise to two bases. Let’s explore if life originated from an unexpected molecule that hardly measures a few nanometers.
Countering the Central Dogma of Life
Studying the evolutionary background is the only way to understand the processes in a human cell. We can all agree that the most essential of all such processes is genetics which starts from a DNA molecule, converted into RNA, and later into proteins. This is the central dogma of life that science has believed over the years, but the RNA world seems to counter it with some intense arguments.
What is the RNA World Hypothesis?
What came first? DNA or RNA? The chicken-egg paradox of life might have been solved with the concept of the RNA world hypothesis that answers many unanswered questions about the beginning of life. A chemist specializing in the chemistry of origin of life, Gerald Joyce produced his work “Very Pretty Chemistry,” which gave us a different perspective of looking at life and its start.
There are two distinct aspects of life: self-sustainment following the Darwinian evolution of life. This self-sustainment might have come from genetic molecules that coded for functional molecules and together carried on life.
Synthesis of RNA in Primitive Earth Conditions
A new synthesis path shows how conditions on early Earth could have given rise to two RNA bases instead of what we have been studying in the Central Dogma of Life. Chemistry supports the claim of the formation of RNA molecules in the primordial soup in early conditions on Earth.
John Sutherland and his colleagues created a ribonucleotide molecule in simple conditions that might have existed on Earth in the primitive ages. Still, they only managed to create 2 out of 4 bases: cytosine and uracil called the pyrimidines. For the other two purine bases, arginine and guanine, Leslie Orgel and colleagues were able to suggest the possible route for the creation of their double-ringed structures.
RNA World is Easy
Simple steps and simplest ingredients; hydrogen cyanide and water, might be all that brought life to Earth. Hydrogen cyanide is believed to be abundant on Earth in early times, and it only contains three molecules of Carbon, Hydrogen, and Nitrogen. The other large molecule at that time? Water.
The chemistry of both these molecules is highly reactive to produce amino-pyrimidines as a result, that have amines in them. Here you have pyrimidines and amines, but what about purines?
Another simple ingredient, also abundant on Early Earth, Acid, solved that question as well. Adding acid to this simple reaction created a precise lone reactive amine. These reactive amines are believed to react with formamide or formic acid, but is there any evidence of their presence on early Earth?
The Rosetta space probe detected the presence of these chemicals on a comet in 2019. This discovery got the scientists thinking that it might have rained on planet earth in primitive times. These bonds lead to a ‘domino cascade’ for producing purines in large quantities.
The Mystery in RNA World Hypothesis
There are four building blocks of RNA: Cytosine, Guanine, Adenine, and Uracil. The formation of C and G, the pyrimidines, was proved earlier, and later the production of A and U, the purines, were also demonstrated by another set of scientists. This leads to a significant development of the RNA hypothesis, but still, a mystery curtails.
The chemical conditions that produce pyrimidines are not the same as those of purines. Also, how Cs and Gs combined with As and Us to give rise to RNA molecules is still not clear. What was the driving force for the formation of complete RNA molecules even if all four bases were there simultaneously?
The RNA world is the twist in the story of the origin of life and has come a long way, but to prove it entirely, scientists have to uncover more secrets to see the domino effect that led to the origin of life through the simple RNA molecule.
- Alberts B, Johnson A, Lewis J, et al. Molecular Biology of the Cell. 4th edition. New York: Garland Science; 2002. The RNA World and the Origins of Life. Available from: https://www.ncbi.nlm.nih.gov/books/NBK26876/
- Van Noorden, R. RNA world easier to make. Nature (2009). https://doi.org/10.1038/news.2009.471
- Orgel LE. Prebiotic chemistry and the origin of the RNA world. Crit Rev Biochem Mol Biol. 2004 Mar-Apr;39(2):99-123. DOI: 10.1080/10409230490460765. PMID: 15217990.
- Kasting J. F., Earth’s early atmosphere. Science 259, 920–926 (1993).
Aqsa Ayub is a content writer, currently working remotely in tech and science with a UK-based company. After completing her bachelor’s from Quaid-i-Azam University. She is doing her Master’s in Industrial Biotechnology from NUST. Aqsa aims to learn more and exhibit new ideas in her writings.