Polymers and the not-so-secret secret of life. Part I The key properties of polymers

The Dec 29th installment of one of our favorite BBC programs, the Radio4 program, In Our Time, was a very understandable and informative discussion of macromolecules.  Mostly it's about macromolecular polymers, that is, long strings, atoms or submolecules, consisting sometimes of millions of such units--things like plastics, polysaccharides, starches, and so on, but some of the discussion links the concepts to proteins, with a brief mention of DNA and RNA.

The discussion is largely about industrial synthesis of macromolecules for various purposes, and is very interesting in its own right.  It only briefly mentions the fact that life is driven not just by polymers but also mentions something that is fundamentally important to life: unlike other polymers that are strings of the key polymers in life, proteins and nucleic acids (DNA and RNA) are composed of different molecules strung together to work as one.  Therein lies the secret of life even if its so un-secret that every biologist knows it very well, and its even taught in good high school biology courses.  Yet this not-so-secret seems to have been badly under-appreciated when it comes to understanding a basic fundamental aspect of life, much more pervasively important than natural selection (we feel), and that underlies what we mean when we say that life is all about cooperation.  That's one of our hobby-horses, a main them in our book, and one we perhaps too often bore MT readers with.

In our usage, 'cooperation' is a double entendre.  First, we use it as an antidote to the cavalier way in which so many biologists and popular writers invoke Darwin and view the world thoroughly in terms of competition.  But secondly, we use the term in its less provocative connotation, but its more literal meaning of co-operation (the word used to be written in a way that denotes this origin: coöperation).  Cooperation means things work when they work together, and nothing reflects and, indeed, enforces this more than the polymer nature of DNA, RNA, and proteins.

These macromolecules are strings of choices of different molecules rather than repeats of the same.  In DNA and RNA its a choice among the 4 nucleotides (A,C,G, and T [U in the case of RNA]).  Proteins are strings of amino acids, of which cells have 20 to pick from, and which DNA codes for in specifying protein structure.  Three key facts are key to making life a phenomenon of cooperation.

• First, the length of the strings is basically not limited.  A DNA molecule (chromosome) can be hundreds of millions of nucleotides long. 
• Second, it is the arrangement and order of these chosen units that give them their properties, which function because
• Third, the arrangement of the sequence determines the function of that sequence because of the way the elements interact with other molecules.

These three properties of polymers make life a polymer phenomenon.  As we went into at length in our book MT, this is because of the way that the chemical 'shape' of the arrangement determines what the molecule will interact with, either among parts of the same long snake of a the protein or RNA, or between it and other molecules.  A protein or RNA molecule fold up upon themselves into a shape, and with properties, that depend on the location of the various different 'beads' in their string, because these 'beads' can chemically attract or repel each other.  And DNA functions by similar matching of its particular sequence of nucleotides with other molecules that can recognize the sequence and bind to the DNA.  Without this kind of interaction DNA and even protein molecules are not 'alive' and don't do anything.  Indeed, the way the universe is assembled, doing something means interactions.  Interactions--cooperation--is the very essence of life.

So we've gone on long enough here.  We'll just finish by saying that interaction in this context is what makes life what it is which is why we stress cooperation, as we'll discuss in Part II.