Each of the 46 DNA molecules in a human cell is approximately two nanometers in diameter and if added together would be approximately two meters in length when stretched out like a taut string. Scaling these dimensions up by a factor of one billion, the resulting structure resembles a railroad track that is two meters wide by two million km long with cross ties positioned about every two-thirds of a meter along the track. This rather closely approximates a true railroad track. Consider that there is a total of around 375,000 km of railroad track in the United States and we see that our metaphoric expression of the human genome is perhaps five times as large; a truly huge structure. Moreover, it is a characteristic of the railroad track infrastructure within the United States that we can perceive it as a long, linear structure, but of course, it is comprised of many discrete segments. DNA is similar in this regard as it is subdivided into the well formed, discrete sections called chromosomes that we mentioned above. Moreover, when we look ever so generically at how DNA processes actually work, we see that they most generally make use of only small sections of the entire genome. This bears significant similarity to the structure of computer memories. We’ll come back to this point when we consider computer memory in subsequent chapters.

What is most appropriate about this metaphorical representation of DNA is that it illustrates some sense of the volume of information that can be conveyed by a single molecule of DNA. For example, three nucleotides convey sufficient information for a cell to specify one distinct amino acid from a set of 20 such amino acids. Amino acids in turn are the building blocks of proteins, and proteins are the building material for living cells of all types. The human genome must convey sufficient information to construct all of the material that comprises the human body as well as provide instructions for how much of each material is to be produced and how it all fits together. The metaphorical illustration offers at least some plausibility that this requirement is well met. Well actually, if it is not met, then there must be some other design or policy mechanism besides DNA involved in the replication of organic life. For the moment, we choose not to pursue that path.

DNA is replicated according to basic interactions among constituent components that are driven by properties of the electromagnetic force between elementary particles modulated by the conservation of energy. To leap ahead just a bit, such interactions are an effectuation of policy established by the electromagnetic force. In the case of DNA, the process is a marvelous dance of recursive interactions of nucleotides with a large dose of parallel processing thrown in. It is through the replication process that characteristics and capabilities of organic structures based on DNA are remembered and subsequently passed on to the descendent organism’s DNA; and hence, to the next generation individuals of the species. Following replication, through which DNA acts as an historical archive of the construction of the generation that went before, DNA then acts as the construction blueprint for the building of the next generation.

In the lifecycle of living things, new generations of organic material are created from time to time; this is what living things do. It is the essential, unique characteristic of life. It is the derivation of the lifecycle metaphor itself. The DNA molecule participates in this creation process through division and replication of itself. Within a cell, a chemical compound called adenosine triphosphate provides a source of energy for the formation of new chemical compounds, including the DNA replication process itself. The cell also contains a reservoir of nucleic acids and other constituent components of DNA. When sufficient energy is available, the two rails of the DNA molecule separate into single strands with a single base of each cross-tie remaining connected to each rail. This process is interesting to us in that it provides a point, actually a multitude of discrete points, within the processing of living material at which very small changes, changes perhaps at a single molecule level, can have very profound subsequent effects because the change

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