Our DNA encodes for only ~20 amino acids out of about 500 known.

Our DNA encodes for only ~20 amino acids out of about 500 known. Why? This article suggests that after more than about 20 they are too similar to each other and you start getting mistaken identity. 20 seems like about the right balance between high enough variation and low enough error rate.

(Hopefully I summarized that about right. This topic is far from my areas of expertise…)

Originally shared by Ciro Villa

Scientists discover the reason for the organic limits on the viability of life (as we know it), and it is “a limitation imposed by shape”. The study is: “Saturation of recognition elements blocks evolution of new tRNA identities”

“A limitation imposed by shape:”

 ” Saturation of the genetic code has its origin in transfer RNAs (tRNAs), the molecules responsible for recognising genetic information and carrying the corresponding amino acid to the ribosome, the place where chain of amino acids are made into proteins following the information encoded in a given gene. However, the cavity of the ribosome into which the tRNAs have to fit means that these molecules have to adopt an L-shape, and there is very little possibility of variation between them. “It would have been to the system’s benefit to have made new amino acids because, in fact, we use more than the 20 amino acids we have, but the additional ones are incorporated through very complicated pathways that are not connected to the genetic code. And there came a point when Nature was unable to create new tRNAs that differed sufficiently from those already available without causing a problem with the identification of the correct amino acid. And this happened when 20 amino acids were reached,” explains Ribas. “

“A study performed at IRB Barcelona offers an explanation as to why the genetic code stopped growing 3,000 million years ago. This is attributed to the structure of transfer RNAs—the key molecules in the translation of genes into proteins. The genetic code is limited to 20 amino acids—the building blocks of proteins—the maximum number that prevents systematic mutations, which are fatal for life. The discovery could have applications in synthetic biology.

Nature is constantly evolving—its limits determined only by variations that threaten the viability of species. Research into the origin and expansion of the genetic code are fundamental to explain the evolution of life. In Science Advances, a team of biologists specialised in this field explain a limitation that put the brakes on the further development of the genetic code, which is the universal set of rules that all organisms on Earth use to translate genetic sequences of nucleic acids (DNA and RNA) into the amino acid sequences that comprise the proteins that undertake cell functions.”

Read more at: http://phys.org/news/2016-05-discovery-fundamental-limit-evolution-genetic.html

The study: A. Saint-Leger et al. Saturation of recognition elements blocks evolution of new tRNA identities, Science Advances (2016) http://advances.sciencemag.org/content/2/4/e1501860

Image: 3D respresentation of a transfer RNA (tRNA). These molecules are crucial for the translation of genes into proteins and they are also the reason why the genetic code cannot exceed 20 amino acid. Credit: Pablo Dans, IRB Barcelona

#science   #life #dna #rna