8. RNA World Hypothesis

One of the challenges in studying abiogenesis is that the system of reproduction and metabolism utilized by all extant life involves three distinct types of interdependent macromolecules which are DNA, RNA and Proteins. But the properties of RNA make the idea of the RNA World hypothesis conceptually plausible, through its general acceptance as an explanation for the origin of life requires further evidences.

While, like protein enzymes, RNA can be act as an enzyme like rybosomes which is known to form efficient catalysts that can catalyze chemical reactions that are critical for life and has the ability to self-replicate or synthesize other RNA molecules. Whereas, RNA is a very similar molecules to DNA with only two major chemical differences that the backbone of RNA used ribose instead of deoxyribose in DNA and one of its nucleobases is uracil instead of thymine in DNA. But the overall structure of RNA and DNA are similar so that one strand of DNA can bind together with one strand of RNA to form a double helical structure which makes the storage of genetic information can be possible in RNA.

In addition to these, RNA can also act as a regulators called riboswitches which can regulates the gene expression particularly in bacteria, plants and archaea in respond to the environmental changes. For example; RNA thermometers regulate gene expression in response to the temperature changes.

Alexander Rich

Walter Gilbert

In fact, Alexander Rich, an American biophysicist first proposed the concept of RNA World in 1962, which states that the RNA World is a hypothetical stage in the evolutionary history of life on Earth, in which self-replicating RNA molecules proliferated before the evolution of DNA and proteins. In 1986, an American biochemist, Walter Gilbert coined the term as the “RNA World Hypothesis”. And this hypothesis is supported by RNA's ability to store, transmit and duplicate genetic information, as a DNA does. RNA can act as a ribozymes, a special type of enzyme. Because of RNA's ability to perform the tasks of both DNA and enzymes, RNA is believed to have once been capable of supporting independent lifeforms. While supporting the RNA World hypothesis, the concept of protocell has been proposed during those time.