DNA

Another post that I wrote some time ago.  With my studies in biochemistry now under way, I am ready to publish it.

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Ever since Watson and Crick described the structure of deoxyribonucleic acid we have been fascinated with the chemistry of life.  Their description of the spiral molecule. the sugars of its backbone, and the structure of the bases that make up the ladder holding the spiral together has fired the imagination of physicists, chemists, biologists, mathematicians and philosophers for the last half-century and will continue for centuries to come.

And I should add programmers.  For the DNA code is just that -- a program for how to duplicate itself and the body whose cells it inhabits.  All done with 4 bases, Adenine, Cytosine, Guanine and Thymine, the pairings they make across the double helix of the DNA molecule, and the triplets of such pairings that encode, with the help of RNA, for the production of amino-acids.

Recently is was announced that a Shakespeare sonnet had been encoded in DNA!  Now this is not to say that the sonnet could be reproduced from the DNA in a normal biological process.  But using a suitable interpreter, the sequence of base pairings could be interpreted as an alphabetic sequence, as the alphabetic sequence of a particular sonnet.

All of this is miraculous enough -- rather since the hand of god has no involvement in the process, wondrous enough, but what intrigues me today is the energy involved in the process.  Everything in the replication of DNA conforms to chemical and physical rules.  These rules are well understood, in terms of the conservation of energy, in terms of the energy of chemical bonds, in terms of exo- and endothermic reactions.  Adenosine Tri-Phosphate for instance is created in an endothermic process, with a catalytic enzyme (tautologic, all enzymes are catalysts) - ATP synthase, inside the organelle mitochondrion.  Each ATP molecule is then transported across our animal cells to a location where its energy can be released, in an exo-thermic reaction further modulated by another enzyme, resulting in the production of ADP, Adenosine Di-phosphate.  ADP then migrates back across the cell to a waiting mitochondria where it is recycled back into ATP.

None of this is orchestrated.  None of it is planned or designed.  But it happens.  And it happens in such a way that the cell lives, respires, transpires, and reproduces.

And it happens in such a way that the exchange of energy in each step of the process, conforms to the rules of the first and second laws of thermodynamics: energy is conserved and entropy increases.

Yet in that simplicity, lies the success and multiplicity of life.  Life exists because it survives.  There is no other reason.  If cells did not (and indeed do not) survive, then there are no more cells, and there is no life.  Life is basic survival, at a microscopic cellular level.

This fact of survival, argues for a remarkable energy transport system within the cell, a transport system that in many life forms exists through several stages of development, and in some species through several generations.

In the case of insects, their DNA defines development through egg and larval stages before the adult creature completes a reproductive cycle.  In the case of some butterflies, such as the Monarch, many generations are involved in a complex life cycle covering continents.  In the case of Homo Sapiens, our DNA describes our embryonic development as well as much of our adult behaviour.

All described by DNA.  All requiring the simple physical processes of energy transfer through enzymatic chemical reactions deep within the cells of all living creatures.

I find it hard to believe that DNA accomplishes this alone.  Certainly, DNA codes for the production of amino-acids.  But there is more than amino acids involved in our metabolism.  DNA only succeeds in a cooperative sense with the rest of the mechanisms inside a cell.  Without mitochondria there would be no ATP.  Mitochondria we know are transmitted through the female egg -- there are no mitochondria in a sperm cell.  What of the other organelles, the Golgi body, ribosomes, centrioles and so on.  Are they inherited or produced as a result of the fusion of egg and sperm, from the DNA?  What is the role of so-called junk DNA?  Is it really junk, or are there other translation processes that we have yet to identify?

My projection is that there is much more to be discovered about the mechanics of life, that will continue to astound us in the years ahead.