Levene's Tetranucleotide Hypothesis
Following
establishment that nucleic acids were localized in the
chromosomes, early
experiments suggested that
the four base molecules
A C G T
occur in approximately equal
ratios.The Russian-American biochemist Phoebus Levene
(1869-1940), who had discovered ribose
sugar in 1909, and went on to discover deoxyribose sugar in
1929.
Leven suggested the structure of nucleic acid as a
repeating
tetramer, based on a repeating phosphate
-
sugar - base unit that he called a nucleotide. The
simplicity of this structure implied that nucleic acids were
too
uniform to contribute to complex genetic variation. Attention
thereafter
focused on protein as
the
probable hereditary substance.
Note
that
in the tetranucleotide model,
adjacent sugar
molecules are
connected by a 3'-5' phospho-diester linkage,
just as in the
Watson-Crick
model. However, each four-nucleotide component is a separate
molecule,
and the bases are directed to the outside.