Evolution of life: ‘selfish gene’ vs ‘selfish ribosome’
The key concept of the ‘selfish gene theory of evolution’ is that cells and organisms exist as mere packages to protect and transmits the genetic information encoded in the DNA. New research recently published in the Journal of Theoretical Biology suggests that is not really the DNA that is selfish but rather the ribosomes. This new discovery forces us to reconsider what we know about the evolution of life.
Ribosomes are large and complex molecules found within living cells. Their role is to translate the genetic information from the DNA into the proteins that perform the cell functions and make up most of its structure. Up to know, the accepted theory was that the ‘aim’ of the DNA is to replicate itself and it would do that by means of the ribosome. In their latest study, authors Meredith and Robert Root-Bernstein from Aarhus University (Denmark) challenged this idea. Their point is quite simple. Like any other system in nature, DNA wants to be in the lowest energy conformation – as much as a ball is more likely to sit at the bottom of the valley (stable equilibrium) rather than sitting at the cusp of the mountain (instable equilibrium). For DNA this means being ‘curled up in a knot’ rather than ‘uncurled and unzipped’, which is its configuration during gene replication and translation. Based on this assumption, Dr. Meredith Root-Bernstein proposes that it is instead the ribosome’s aim to replicate the genes as its ‘resting position’ is ‘ready to translate DNA into proteins’.
Ribosomes are composed of proteins and RNA. RNA is structurally very similar to DNA and exists in three forms. One form of RNA is ribosomal RNA (rRNA), which is structural, forming the scaffold of the ribosome. Two other kinds of RNA, messenger RNA (mRNA) and transfer RNA (tRNA), are outside the ribosome and are functional to assembling proteins from DNA instructions. Specifically, the mRNA transcribes the genetic information from DNA and carries it to the ribosome while the tRNA translates the mRNA message into amino acids, which are strung together on the ribosome to make a protein.
The new hypothesis of the ‘selfish ribosome’ proposed by daughter and father Meredith and Robert Root-Bernstein was tested by comparing ribosomal RNA to databases of RNAs, DNA and proteins of the bacteria E. coli. If ribosomes wanted to reproduce themselves, the rRNA would have to satisfy three criteria. Firstly, it would have to contain the ‘genes’ encoding its own ribosomal proteins for functional purposes. Secondly, it would have to contain the mRNAs needed to carry its own genetic information. Finally it’d have to encode the tRNAs necessary to translate the mRNAs into proteins. Meredith and Robert Root-Bernstein showed that the structure of the rRNA shows remarkably good matches to all of these structures in E. coli. “We have demonstrated that rRNA contains the vestiges of the mRNAs, tRNAs and ‘genes’ that encode its own protein structure and function. Ribosomes are not simply the passive translators DNA” – says Dr. Robert Root-Bernstein.
These results interestingly put evolution in a whole new perspective. To put it in the words of Dr. Meredith Root-Bernstein: “Maybe the selfish ribosome puts a new spin on feeling kinship with other creatures. We are all just different kinds of homes to the ribosomes!”
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