In all living things, proteins are the workhorses inside the cell. They build structures, regulate processes, transport materials, and take part in virtually every function of cellular life. Well over 100,000 different types of proteins have been found in the living kingdom, and each of them is created by using just 20 different types of amino acids arranged as building blocks in a particular order. Changing the order of the amino acids changes the type of protein being created, and while an average protein might be made up of 200-400 amino acids, others have thousands. Living cells know how to arrange the order of these amino acids by reading the information encoded in their DNA.
In order to encode this information, four different types of nucleic acids (adenine, thymine, guanine, and cytosine – A,T,G,C) are used to form individual representations called “codons”. A codon can be thought of as a "code word" inside the cell. Each of these code words is made up of three nucleic acids (triplets) which are read together as a single representation. For instance, the triplet TAC is translated by the cell to add an amino acid called tyrosine to a new protein being created. CTA means add leucine, GTC means add valine, CCG means add proline, GAC means add aspartic acid, and so on. This is how the cell builds every protein in the living world - it uses a code.
The Input of Information
When the cell manufactures a new protein, it starts the process by locating the correct segment of its DNA for building that particular protein. The sequence of codons in that segment are then copied into a secondary mobile medium called "messenger" RNA (mRNA). When the information is copied into RNA, the nucleic acid thymine is substituted with another nucleic acid called uracil, but the pattern of the codons remains the same. This RNA copy is then matured and transported to the site of protein assembly, which is a molecular structure called a ribosome. Upon entering the ribosome, the sequence of codons in the messenger RNA are used to arrange the order of another set of RNA molecules called "transfer" RNA. These tRNA carry with them the individual amino acids that will be used to build the protein.
In short, the information in DNA is first copied into mRNA, and the mRNA is then used to order tRNA (with their amino acids in tow) in the same sequence as it existed in the original DNA. After all the amino acids are bound together in the right sequence, the chain of amino acids is then folded up into the protein that the cell needs to survive.
The Point of Translation
The input of information into the ribosome results in amino acids being attached together in a sequence prescribed by the DNA. Each critical step in this process is controlled by purely mechanical (deterministic) forces. However, in order for the genetic system to translate the form of a protein through the medium of nucleotides, the system cannot rely on deterministic forces alone to achieve that result.
To achieve translation, a set of arbitrary relationships must be established in the operation of the system, and these relationships can only exist if the various codons are mapped to their amino acids while the discontinuity (i.e. the arbitrariness) between them is preserved. This requires the system to be organized in a specific way to bring those relationships into being. Inside the cell, this organization is accomplished by isolating the establishment of the code from the translation of the codons.
In the genetic translation system, the relationships that make up the genetic code are established by a very special set of twenty complex proteins called aminoacyl tRNA synthetase (aaRS). The aaRS are the physical protocols in the genetic translation system. It is their job to load the correct amino acids to each of the tRNAs, and they accomplish this task prior to the tRNA ever entering the ribosome. Therefore the establishment of the genetic code is both spatially and temporally isolated from the remaining translation process. One process (the input of form) is functionally coordinated with the other process (the establishment of an effect) yet the two processes remain independent. The contingent organization of the system thereby establishes the genetic code while maintaining the discontinuity that is vital to its function.
A living cell is a heterogeneous system. It requires discrete parts in order to function, and reproduces itself by means of prescriptive synthesis. This process requires the translation of an informational medium. The minimum requirements for the origin of the system are therefore established by what is physically necessary to record and translate the amount of information that the system needs to successfully describe itself into memory.
A physical analysis of the system makes explicit what those requirements are.
The necessary material conditions of genetic translation are found to be exclusively identifiable among all other physical systems. They can be identified nowhere else in the physical world except in recorded language and mathematics – two universal correlates of intelligence.
Watch a Video of the Process (2.5 min)