Biology Reference
In-Depth Information
working a clock has remained in models for molecular biology with
the notion of stereospecificity.
Between 1950 and 1970, two series of work helped formulate a
theory explaining the construction of a phenotype from genetic
information. In the first instance, protein synthesis was elucidated,
with the discovery of the transcription of genes into RNA and the
translation of RNAs into proteins. In the very strong genetic deter-
minism which reigned at the time, this led to the 'central dogma of
molecular biology' enunciated by Francis Crick (1958), which
asserts that genetic information can only be transferred in one
direction, from the DNA to the proteins, with no possibility of it
being transferred back to the DNA. This therefore prevents the
organism from influencing the genome in any way and gives DNA
absolute power over biological processes. Secondly, the molecular
interactions involved in morphogenesis and the regulation of bio-
logical systems were analysed. The existence of a property of stere-
ospecificity 17 was then advanced. The concept arises from the lock
and key model suggested by Fischer in the 19th century for defining
relationships between an enzyme and its substrate (Fischer, 1894).
It has been used in immunology to explain recognition by an anti-
body of its antigen. Then, as Jacques Monod (1910-1976) explained
in Chance and Necessity (1970), it has been generalised to all
molecular interactions, including those involved in morphogenesis,
cell signalling and the regulation of gene expression (CN pp. 61-64,
74-80, 82-93).
A protein is formed by the folding of the linear chain of amino
acids synthesised from its gene. In theory, this folding produces one
single three-dimensional structure for each protein. According to
the principle of stereospecificity, a protein would therefore have a
stable, ordered, three-dimensional structure which would strictly
determine how it functions and the possibilities it would have of
combining with other proteins (Wu, 1931; Mirsky and Pauling,
17 Etymologically stereospecificity means 'solid specificity', i.e. specificity in the
material relationships between molecules. The concept of specificity itself comes
from Aristotle's philosophy (see chapter 2, ยง2.2.3).
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