Biomedical Engineering Reference
In-Depth Information
less random. The life greatly depends on order and the master code of a living
organism has to consist of a large number of atoms. The living organism seems to
be a macroscopic system, the behavior of which approaches the purely mechanical
(as contrasted with thermodynamical) conduct to which all systems tend, as the
temperature approaches absolute zero and the molecular disorder is removed. The
life is based on ''order-from-order'' principle. Schrodinger indicates that a periodic
crystal is the material carrier of life, in contrast to periodic crystal of classical
(inanimate) physics [3].
The asymmetry of living bodies was emphasized first by Louis Pasteur, who
widely used examples with spiral structures. Upon examination of the minuscule
crystals of sodium ammonium tartrate, Pasteur noticed that the crystals came in
two asymmetric forms that were mirror images of one another (1849): solutions
of one form rotated polarized light clockwise, while the other form rotated light
counterclockwise. As a result, he devoted himself to the study of what he called
dissymmetry
, pointing out that inorganic substances are not dissymmetrical in their
crystallization, while all the products of vegetable and animal life are dissymmetric.
He concluded that there was some great biological principle underlying this: ''All
artificial products of the laboratory and all mineral species are superposable on
their images. On the other hand, most natural organic products (I might even say
all, if I were to name only those which play an essential part in the phenomena
of vegetable and animal life), the essential products of life, are asymmetric and
possess such asymmetry that they are not superposable on their images'' [4, 5].
Geometry itself makes distinction between living and inanimate bodies, and this
difference protects the autonomy of life. In the bone, both seemingly opposite
substances, living and unliving, meet together and cooperate toward creating bone
tissue.
This is the problem of three-dimensional growth through spiral forms, discussed
in 1884 by Lord Kelvin [6], who earlier proposed (1873) the term
chirality
,cf.[7]and
[8]. The repetition of such a way of development is observed from molecular level
until macroscopic forms. In nature, helical structures arise when identical structural
subunits combine sequentially, the orientational and translational relation between
each unit and its predecessor remaining constant. A helical structure is thus
generated by the repeated action of a screw transformation acting on a subunit. A
plane hexagonal lattice wrapped around a cylinder provides a useful starting point
for describing the helical conformations of protein molecules, investigating at the
same time the geometrical properties of carbon nanotubes, and certain types of
dense packings of equal spheres.
Essential for life proteins are organic compounds made of amino acids that
are arranged in a linear chain and joined together by peptide bonds between
the carboxyl and amino groups of adjacent amino-acid residues. The sequence of
amino acids in a protein is defined by the sequence of genes that is encoded in the
genetic code, which specifies 20 standard amino acids. The collagen is the main
protein of CT in animals and the most abundant protein in mammals.
Among the substances, some are ungenerated and imperishable, while others
partake in generation and perishing. Linus Pauling in 1970 indicated several
