Counting on the Tree of Life

[xchrom]

http://www.elpais.com/articulo/sociedad/Counting/on/the/Tree/of/Life/elpepusoc/20110726elpepusoc_13/Tes

An octopus can count; some birds can count; you can count; but is it possible that your DNA can also count? Can this ability be related to the origin of life on earth? Recent studies I have performed with Diego L. Gonzalez (Institute for Microelectronics and Microsystems, Italian National Research Council) and with Rodolfo Rosa (Statistics Department, University of Bologna), show that this apparently innocent question might lead to a significant advance in our understanding of how life manages genetic information. In brief, this management consists of three main steps, 1) replication: the DNA molecule (where all our genetic information is stored, like the hard disk of a PC) is duplicated just before cell division; 2) transcription: one strand of the double helix of DNA is copied forming a single strand RNA; 3) translation: the mRNA (messenger RNA) is translated into proteins. This latter step is performed using the translation table known as the genetic code. In this way, each codon, a piece of mRNA consisting of three consecutive bases, is translated into one of the 20 amino acids that constitute the building blocks of proteins. There are four such bases in RNA, Uracil, Cytosine, Adenine, and Guanine (U, C, A, G).

At this point a first answer to our question can be given. In fact, DNA replication is performed one base at a time. Moreover, in the transcription step, when an error is produced, the machinery stops and goes back five bases. Finally, protein translation implies counting bases exactly in multiples of three. Thus, the complex genetic machinery requires an intrinsic counting capability. Furthermore, as the studies report, also the genetic code is closely linked to counting. In fact, counting is at the basis of numeration systems, and is, consequently, at the basis of mathematics. For representing integer numbers, usual numeration systems adopt the powers of a base, for instance, 10 in our standard decimal system, or 2 in the binary one mainly used by computers. But these numeration systems are univocal, that is, any integer number has one and only one representation. In contrast, the genetic code is redundant (not univocal). Specifically, a given amino acid can be represented by more than one codon, therefore, the usual numeration systems are of little relevance for dealing with the genetic code.

[Leopolds Ghost]

1. Interesting!

Paging Darren Aronofsky... or Terrence Malick.