Abstract
Biological information is one of the most important characteristics of life, and it enables life to evolve to higher complexity and adapt to the environment by mutation and natural selection. However, the origin of this information recording and retrieval system remains a mystery. To understand the origin of biological information will lead us to one step closer to understand the origin of life on earth. Biological information is encoded in DNA and translated into protein by the ribosome in all free living organisms. The information has to be translated into proteins to carry out its biological functions, so the evolution of the ribosome must be integrated with the development of biological information. In this article, I propose that the small ribosomal subunit evolved from a ribozyme that acted as an RNA helicase in the ancient RNA world, and the involvement of tRNAs and the large ribosomal subunit evolved to enhance the helicase activity and to overcome the higher energy require-ment for high GC content RNA helices. This process could have developed as a primitive recording mechanism: since Watson-Crick base paring is a natural property of RNA, each time the proto-small ribosomal subunit came to a particular GC-rich helix, tRNA-like molecules and the proto-large ribosomal subunit would have to be engaged to generate the helicase activity, and consequently the same polypeptide would be synthesized as a by-product. Simple recorded messages then evolved into useful biological information through continuous mutation and natu-ral selection. This hypothesis provides logical and incremental steps for the development of programmed protein synthesis. I also argue that the helicase activity is preserved in the modern ribosome and that from our knowledge of the ribosome, and we can deduce the possible mechanisms of the helicase activity.
Highlights
Biological information is contained in all the genes and intergenic regions with signals for gene expression
They found that the translation rate is greatly influenced by the G + C content of folded structures in the mRNA at the ribosomal entry site. These findings indicate that the modern ribosome is still an mRNA helicase, and that the helicase activity is directly linked to the inter- and intra-subunit conformational changes during an elongation cycle
As a result of this movement the L shaped tRNA acts like a spring with one end bound to mRNA through the Watson-Crick base pairing and the P site of the small subunit and the other end interacts with the E site of the large subunits
Summary
Biological information is contained in all the genes and intergenic regions with signals for gene expression. There are two major types of genes: one encodes information that is expressed as functional RNA molecules such as rRNA, tRNA, and snRNA, and another encodes information for protein synthesis expressed as mRNA. Since a gene can only carry out its biological function after it is translated into protein by the ribosome, the understanding of the evolution, structure and function of the ribosome should lead to an understanding of the origin of genetic information. Transfer RNA (tRNA) is one of the key substrates in protein synthesis, and has an L-shaped structure with an anticodon at the end of one (anticodon) arm and a specific amino acid is linked to the end of the other (acceptor) arm (Figure 1(b)). Within the small ribosomal subunit the anticodon interacts with a codon on the message RNA (mRNA) by Watson-Crick base pairing and this process is called tRNA selection or decoding. When the cognate tRNA is selected, it delivers a specific amino acid into the pepti-
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