Towards understanding the origin of genetic languages
Indian Institute of Science
April 13 2007
In: Quantum Aspects of Life Eds. Derek Abbott, Paul Davies, & Arun Pati
The author views molecular biology as a nanotechnology and as a system for acquiring, processing and communicating information. The kinds of processing seen in DNA and in proteins are argued to be the optimal solutions for the information processing that they carry out.
Patel stresses that life is a non-equilibrium process. Metabolism, a series of biochemical processes, is a basic feature of living matter. This processing requires the continuous extraction of free energy from the environment. The manipulation of information is seen as determining the complex structures that make up life.
The information processing of living matter is seen as needing a language that uses a set of building blocks, whose arrangements confer different meanings. This language has to be protected against errors, and to make efficient use of physical resources. Genes and proteins constitute a language with building blocks comprising four nucleotide bases for DNA and RNA and 20 amino acids for proteins. Other nucleotides and amino acids exist in living cells, and the selection of these particular four and twenty building blocks is taken to indicate the selection of a language. Minimisation of error leads to the selection of a digital language with building blocks with discrete operations. The genetic language has a tiny error rate ensuring stability, but with no errors, there would be no change through mutation. In protein, carbon atoms can form aperiodic structures which can encode a language. The amino acid chains are formed in one dimension which is simplest, but can then be folded three dimensionally.
There have been various attempts to explain the emergence of this language in evolutionary terms. Crick (1968) made the hypothesis that the language came into existence at one go, which seems merely to repeat the improbability problem of the emergence of replicators. In contrast, Patel favours the idea that the language evolved through a trial and error process, until it reached an optimal solution. A binary system of two nucleotide bases, similar in concept to modern computers, would be sufficient to encode the genetic information. However, Grover’s algorithm indicates that four bases provides an optimal approach. Patel thinks that this four-base process may have evolved at a later stage, after an initial binary system. P The genetic machinery is seen as having the physical components to implement Grover’s algorithm. The genetic code is based on four nucleotides arranged in triplets that code for 20 amino acids. The optimal number (Q) of sampling operations in Grover’s algorithm for a database (N) is given by Q = 1 for N = 4 and Q = 3 for N = 20. It requires quantum superposition, but not necessarily non-local entanglements. As usual with quantum proposals, the most important question is whether the quantum superpositions could survive for long enough to be useful.