The Irreducibly Complex Ribosome

Ribosome DNA artwork

A unique creation in the three domains of life

by Matyas Cserhati and Warren Shipton

Article from peer reviewed technical “Journal of Creation”

The evolution of the genetic code and the ribosome are intimately connected as the code is expressed through ribosomal activity. Models of genetic code evolution are analyzed. The error-minimization theory is faulty in that it supposes that highly error-prone genetic codes could produce more precise codes over time. The stereochemical theory posits complementarity between nucleotides and amino acids, but cannot demonstrate this for the whole code. The co-evolution theory states that the genetic code developed from an ancestral through an ancient to a modern state. There is no evidence for ancestral code protein generation. The big question remains why the code solidified in its present state. Finally, the accretion theory of ribosomal evolution is shown incapable of answering key questions.

Large and small subunit ribosome proteins are conserved within Archaea, Bacteria, and Eukarya but not between these domains. The size and weight of the subunit proteins are similar between Archaea and Bacteria only, whereas protein types are similar only between Archaea and Eukarya. This implies that the ribosome of all three domains has been created uniquely. The presence of many unique proteins and protein domains in the mitochondrial and chloroplast ribosomal proteins imply that they are not related to prokaryotic ones.

Protein synthesis is a fundamental function in the cell that involves ribosomes. The process involves first the transcription of the DNA sequence to messenger RNA (mRNA). Each sequence of three bases in mRNA is known as a codon. The information contained in the codon is used to produce functional proteins, as each codon specifies a particular amino acid. The vital step in protein formation occurs on the ribosomes with the cooperation of transfer RNA (tRNA) using ribosomal RNA (rRNA) as a binding site. It is evident that ribosomes are prerequisites to the life of the cell in that they convert genetic information into functional proteins. These structures consist of two different sized subunits, whose size is described in terms of Svedberg units (S), which is a measure of the sedimentation rate. Ribosomal proteins dominate these subunit structures, but there are up to 120 different molecules involved: rRNA, mRNAs, tRNAs, ribosomal proteins, aminoacyl-synthetases, and scanning factors. They are all needed to fulfil this basic, yet highly complex cellular housekeeping function. Besides histones (DNA packaging proteins in eukaryotes), ribosomal proteins are the most conserved proteins in the living world.1

The coupling of the protein-translation machinery to the DNA is fulfilled in the genetic code, which consists of four nucleotide bases arranged in groups of three (codon). The codons can be arranged in 64 combinations allowing selection of the 20 amino acids; special codons mark the start and stop point for a protein. Some evolutionists believe that the ribosomes came into being before cellular life and represent the first self-replicating entities. This means the ribosomal RNA they carry is a primitive genome.2

Here we will take a look at one of the greatest problems in biology. Classically, living systems produce copies of themselves. In ancestral systems, evolutionists consider that the descendants were different from their immediate ancestor as they needed to generate coding rules that then went on to evolve new systems.3,4

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image credit: Original artwork from video image by CMI