in more detail in the
following chapter, but for the moment we’ll simply assume a definition of the
term to be a constrained environment of
living and non-living elements that facilitates interactions among its various
components. So, as a start, let’s delve just a bit into the processes of
living things.
We make a
seminal assumption that the repetitive production of some entity, be it organic
or mechanical, requires a design and
a subsequent means to apply policy
through which the operational existence of the entities proceed. The words we’ve
selected might be viewed as slightly provocative, but we will try very hard to
use them carefully. To suggest or even to consider a design does not require
consideration of a designer, either for organic systems or for electrical and
mechanical systems. We suggest that a design is required because it is
difficult, if not impossible, to explain systematic replication without one.
Bear in mind of course, we view it as completely consistent with this
assumption that a design can encompass randomly derived components. A snowflake
is the result of a very well defined design. However, the design includes a
random component inherent in the crystallization of water that renders every
snowflake unique. Taken en masse,
they readily form a blizzard or an avalanche. In a similar vein, as we
suggested in our Prologue, policy is the way we explain or define how things
work. A rock, sitting on a hillside, effects policy. At the very least, it is
subject to the policy established by the basic physical forces. In some cases,
the rock is stationary for a geological age. Then, an earthquake impacts the
rock’s policy infrastructure and it rolls down the hill. So, based on these
assumptions, let us first examine the landscape for living organisms.
Based on deoxyribonucleic
acid or DNA, life has evolved on the earth through a process that an
electronic circuit designer might recognize as a general feedback loop. In the
April, 1953 edition of the journal Nature, James Watson and Francis Crick
published a paper entitled A Structure
for Deoxyribose Nucleic Acid that provided the first definitive description
of DNA’s form. Their model development was apparently enhanced by the x-ray
crystallography of Rosalind Franklin, although she did not participate in
authoring the seminal paper. Crick and Watson found that the molecular
structure of DNA is that of a polymer whose resultant shape resembles a
spiraling railroad track; the famous shape termed a double helix.
The rails of a strand of DNA are comprised of alternating sugar (deoxyribose)
and phosphate molecular components. Much like the cross-ties of a railroad
track, attached to these rails in a perpendicular fashion and at periodic
connection points are pairs from a set of four nucleotide bases: adenine,
cytosine, guanine and thymine. Adenine can only be paired with thymine, and
cytosine can only be paired with guanine. Each such cross-tie is termed a base
pair. One can readily see from this basic architecture that there is a high
degree of systematic chemical as well as mechanical structure in the DNA
molecule.
Drawing for
example from Understanding DNA by
Chris Calladine, Horace Drew, Ben Luisi and Andrew Travers, we learn that the
total DNA complement within a single human cell, typically referred to as the
genome, amounts to approximately three billion base pairs distributed among 46
chromosomes. A single base, when combined with the sugar and the phosphate
radicals, forms a structure termed a nucleotide.
Hence, one can view a DNA molecule as a long sequence of paired nucleotides. At
this point, it might be interesting to draw attention to the metaphor that we
have selected to represent the DNA molecule; that of a railroad track. Most
texts use a ladder metaphor. Our selected theme has some relevance if we
consider the following.
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