Biology Reference
In-Depth Information
4.2 The causes of molecular non-specificity
The principle of stereospecificity, on which genetic determinism is
based, which implies that relationships between biological molecules
are unequivocal, or very limited in number, does not therefore com-
ply with experimental evidence. Biological molecules are capable of
multiple interactions and the number of combinations for them in
one cell is enormous. We have described the non-specificity of pro-
teins. About ten years ago, the role of 'interfering' RNAs in regu-
latory processes was revealed, but in Richard Burian's analysis their
action is subject to the same problem as experienced by proteins.
Their interactions are not specific and generate a huge number of
combination possibilities (Burian, 2008).
The ontogenesis of a single living structure cannot therefore be
the result of a process of self-assembly bringing only molecular
affinities into play, because several structures are possible due to
this number of combinations. Other factors evidently have to come
into effect so that the number of combinations is limited. Before
analysing this problem in the face of genetic determinism, and
envisaging its theoretical consequences, we must discuss the causes
of molecular non-specificity. We will see that they directly contra-
dict the principle of order from order, i.e. the idea that there is a
biological order intrinsic to the living organism which is carried by
proteins.
4.2.1
The multiplicity of interaction domains
Proteins interact via interaction domains, which are structural
motifs, corresponding in general to sequences that are 40 to 150
amino acids long (Hunter, 2000). There are a great number of these
domains corresponding to the different amino acid sequences. One
cause of non-specificity comes from the fact that the same domain
may be carried by many proteins.
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The sequence coding for the
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Even if the context in which a domain is inserted partly restricts its possi-
bilities for binding with other proteins.
