Before DNA, Life Existed in an RNA World
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Before DNA, Life Existed in an RNA World

This article is an explanation for why life evolved to use DNA instead of RNA. The reader should learn that there was a time when RNA, not DNA, acted as the genetic databank for life. This article also explains why it was necessary that evolution would choose DNA, because of its ability to faithfully transmit genes, to become the next databank for genetic material. This was also important because it ensured that organisms were able to pass on the genes that gave them advantages to their offspring.

We all know that DNA (deoxyribonucleic acid) is the genetic material of life. However, you may be surprised to learn that there is sufficient evidence to support the hypothesis that there was a time when RNA (ribonucleic acid), not DNA, was the genetic material of all life on Earth (Joyce, 2002). This means that life, at one time, existed in an RNA world. RNA is structurally different from DNA. In comparison to the DNA structure, RNA is single-stranded, more hydrated (it contains additional hydroxyl group), and uses a different nitrogenous base (Uracil). This begs the question as to why didn't life continue to use RNA as its genetic material?

The answer becomes apparent when the structure of DNA is examined. The most striking difference between DNA and RNA is that DNA is double-stranded. The significance of being double stranded is that one strand of the DNA can act as the template for the other. The reason for this is because the nitrogenous bases that comprise the "ladder" portion of DNA are very specific about what other nitrogenous bases they can bind to. For example, the base Cytosine will correctly bind to Guanine (and vice versa) and not the other DNA bases. This means that if a particular DNA base is damaged or removed from one strand, the other DNA strand can be used to ensure that the correct base is added to its intended position. This mechanism also serves another important function as it ensures the accurate transmittance of genetic material from one generation to the next. Since we know that the game of evolution is played when natural selection chooses certain organisms to pass on their genetic information onto the next generation, it is important that the genes that were necessary for the survival of that organism to remain intact. The double-stranded feature of DNA ensures these genes will be faithfully transmitted to the next generation thereby increasing their odds for survival.

The main problem with RNA as for serving as an organism's database for genetic information is that it is single-stranded. This means that mutations in RNA would not likely be repaired accurately because there is no template that can be used to correct such errors. This has further implications in that if this mutated RNA was used as the genetic material for the next generation of offspring, the genes that enabled the parent generation to survive would not be faithfully transmitted to subsequent generations.

Even with this information, it is important to remember that mutations in general are, for the most part, rare events. The rarity of

mutations would be a reason that would explain how life was able to survive in an RNA world long enough to perpetuate itself to a point where DNA could take over the responsibilities of being the genetic databank of life.

References:

Joyce, G F. “The antiquity of RNA-based evolution.” Nature 418.6894 (2002) : 214-221.

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Comments (1)

awesome ,thanks votes

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