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La Lettre
Jons Jacob Berzélius
(1779-1848)
© Georgios Kollidas - Fotolia
© Alamy
© Leigh Prather - Fotolia
Tridimensional structure of DNA by X-ray diffraction
Francis Crick
(1916-2004)
Fifty years later, the Swedish Berzelius built on Lavoisier’s approach
and proposed a theory according to which any chemical reaction
resulted from the combination of groups of atoms that he called
"chemical radicals
"
. He even invented the term "catalysis
"
to
describe the specific acceleration of a chemical reaction and
called "polymers
"
the “organic” compounds that living beings
produce from these very chemical radicals. A most animated
debate then shook the scientific community. Could one believe
in the vitalist theories that, invoking mysterious forces, claimed a
difference between organic compounds – produced by living beings – and
inorganic substances? The chemical synthesis of urea by Whöler, in 1825, brought a first demonstration
that vitalism had failed; the many organic syntheses performed since then have confirmed such failure.
The repertoire of the molecules that constitute living beings comprises high-weight polymers, or
"macromolecules
"
, including in particular proteins – another term Berzelius coined – which result from
the linear combination of 20 amino acids. Other macromolecules are formed from nucleotides – such as
desoxyribo- and ribo-nucleic acids (DNA and RNA) – , sugars – for polysaccharides – and so forth. In 1833,
it was observed that the enzymes catalyzing the chemical reactions that constitute living organisms were
proteins. Finally, in 1897, Buchner demonstrated that the whole complex processes involved in alcohol
fermentation could be obtained in vitro from an extract of yeast, in the very absence of any living yeast.
The relevant set of enzymes and their substrates were enough. From then on, living beings – including
human beings – would be understood as vast and complex chemical systems in which macromolecules
would play a central role.
Throughout the 20
th
Century, and even today, research has been dealing with the fine structures, at the
atomic level, of these macromolecules. Various physical techniques have been used, including X-ray
diffraction. In 1953, it was the double strandedDNAmodel described byWatson, Crick andRosalind Franklin
that revolutionized our understanding of heredity. It would be followed, more recently, by the elucidation of