J.P. from the UK writes in response to Inheritance of biological information—part II: redefining the ‘information challenge’:

 

The semiotic triad. In genetics, the amino acid is the object that is symbolically represented by the codon, which the cell interprets via the translation mechanism (the ribosome).

Thank you for all the work you put in. Your site is very easy to use, with a wealth of articles. I especially like the “Surprise me” section, where you can browse a random choice.

This article was fascinating, though it was sometimes a stretch to understand, because of my lack of knowledge in this field.

I would be grateful if you could explain the following. It is in the discussion of semiotics, about 2/3 of the way down the article:

“ … the relation between the sign and object is arbitrary and cannot be explained in terms of the laws of physics”

I understand that in many cases the sign and object are indeed according to an arbitrary code (in languages for example—the same meaning can be conveyed in a multitude of different ways); but don’t see how that can be so in the case of the genetic code.

Of course, GOD created DNA, the genetic code itself and the very laws of chemistry and physics that make them work. However, I thought that the actual production of RNA or proteins, from DNA, COULD be explained in terms of the laws of physics.

Surely biological molecules such as DNA operate by a mechanism that depends on the physical configuration of the molecule? The base pairs fit together according to the laws of physics—don’t they???

Dear J.,

Thank you for your feedback.

The operation of cellular machinery obeys the laws of physics without exception. But that isn’t what the author is talking about here. He is talking about how the symbolic meaning of a given DNA sequence is arbitrary because there’s no inherent reason why a specific DNA sequence has to code for any specific message. In the case of DNA, there are four bases (A, C, G, and T). This is not necessary, however, as a base-two system (say just A and G) would equally suffice. The code would look radically different, but the same messages could be spelled out nonetheless. Our computers all run on base-two (zeros and ones) and they operate just fine….

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