RNA stands for the ribonucleic acid, which is one of the two most important nucleic acids in present an organism, the other one being the DNA or deoxyribonucleic acid. Even though RNA is the genetic material in some of the organisms, DNA is considered to be the predominant genetic material in almost all the organisms. According to the RNA world hypothesis, ribonucleic acid is the first genetic material in which all genetic information was stored and the first life had arisen from it. It is known to be a self-replicating molecule. In simple words, the RNA is known to be the precursor to every life form which exists today on the earth. It is believed that the modern cells arose from them and all the essential processes which occur in the living organisms evolved around the RNA. The RNA world hypothesis was greatly accepted by the scientific community. In this article, we will study about the RNA world hypothesis and the RNA world.
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The RNA World Hypothesis is a concept that was put forth in the1960s by Francis Crick, Carl Woese, and Leslie Orgel. It proposes that the earlier life forms might have used RNA alone for the storage of their genetic material.
Walter Gilbert, which was a Harvard molecular biologist, was the first one to use the term "RNA World" in one article that was published in the year 1986. The hypothesis says that the DNA later became the genetic material as a result of the evolution since RNA was a relatively unstable molecule. According to the RNA World Hypothesis, about 4 billion years ago, the RNA was the only primary living substance, largely because of the RNA’s ability to function as both the genes and the enzymes.
The main reason behind the hypothesis is that the RNA is much capable of self-replication and might, therefore, have carried the genetic information across all the generations independently. This concept has been highly debated all across the scientific world for over the last 50 years.
Experts now generally agree that the non-living chemicals could not have given rise to the bacterial cells in one single step and that the intermediate, and pre-cellular life forms must, therefore, have existed. Of all the possible pre-cellular life models that were considered, the most popular one is the RNA World.
In the year 1968, Sir Francis Crick proposed that the RNA would have been the primary genetic material since it is capable of self-replication, owing to its ability for acting as an enzyme. Moreover, the RNA can also be converted to the DNA by the reverse transcription, that further strengthens the idea that the RNA world might have been the initial pathway to the cells.
It was thought previously that the only biomolecules which could catalyze the essential chemical reactions in the cells were the proteins. However, Sidney Altman, Thomas Cech and other colleagues discovered a class of RNAs which is capable of the catalyzing chemical reactions called ribozymes. Altman and Cech were hence awarded the Nobel Prize in Chemistry in the year 1989 for this discovery.
The discovery of the ribozymes supported the RNA World Hypothesis. The strongest argument in proving the hypothesis is probably that the ribosome, which assembles the proteins, is itself a ribozyme. Despite the fact that the ribosome is composed of both the RNA and the protein, the processes involved in the translation are not catalyzed by the protein, but by the RNA, which indicates that the early life forms might have used the RNA to catalyze the chemical reactions before they used the proteins.
Research over the past few years has demonstrated the useful properties of the random RNA sequences, like the production of the active RNA ligases from the random sequences of the RNA. But, this is not enough to prove about the RNA world hypothesis. Based on what is referred to about the present-day organisms, it is not possible to conclude that the self-replicating molecule was the primary source of the catalytic mechanisms that are fundamental to the living systems.
Research on the RNA World Hypothesis is still ongoing, although the recent findings threaten to disprove the hypothesis. NASA stated in one 1996 report that the difficulties which are surrounding the RNA World concept are the chemical fragility of the RNA and its poor range of the catalytic activities.
The biochemist Harold S Bernhardt shares the same kind of concerns and in one 2012 biology paper, he called the concept to be the worst theory of the early evolution of life. His paper states that the complexity of the RNA molecule means that it could not have arisen prebiotically and that the RNA is unstable and that it possesses only limited catalytic properties.
1. What is the RNA World Hypothesis?
Ans. The discovery of the ibozymes supported a hypothesis called the RNA World Hypothesis, which stated that the earlier forms of the life might have relied only on the RNA to store the genetic information and to catalyze several chemical reactions. This hypothesis was proposed independently by Francis Crick, Carl Woese, and Leslie Orgel in the 1960s. This was decades before the discovery of the ribozymes and soon after the double-helical structure of the DNA was determined.
2. What are Ribozymes?
Ans. The central role for several proteins in the cell is catalyzing the chemical reactions which are essential for the survival of the cell. These proteins are called enzymes. Until relatively recently, it was thought that the proteins were the only biological molecules that were capable of catalysis. In the early 1980s, however, the research groups led by Sidney Altman and Thomas Cech independently found out that the RNAs can also act as the catalysts for the chemical reactions. This class of the catalytic RNAs are called ribozymes, and this finding earned Altman and Cech the Nobel Prize in Chemistry in 1989.