2009_Book_FoodChemistry

46 1 Amino Acids, Peptides, Proteins
through second, third and subsequent repetitive
reactions:
1.4.1.5 Derivation of Amino Acid Sequence
from the Nucleotide Sequence
of the Coding Gene
The number of proteins for which the coding gene
in the genome has been characterized is increasing
steadily. However, a considerable part of the
amino acid sequences known today has already
been derived from the nucleotide sequences in
question.
The background of this process will be briefly
described here. The nucleotides consist of four
different bases as well as 2-deoxyribose and phosphoric
acid. They are the building blocks of the
high-molecular deoxyribonucleic acid (DNA).
The nucleotides are linked via 2-deoxyribose and
phosphoric acid as 3 ′ → 5 ′ -diesters. In DNA, two
polynucleotide strands are linked together in each
case via hydrogen bridge bonds to give a double
helix. The bases thymine and adenine as well as
cytosine and guanine are complementary (cf. Formula
1.90). DNA is the carrier of the genetic
information which controls protein biosynthesis
via transcription to messenger ribonucleic
acid (RNA). In translation into proteins, the
sequence of bases codes the primary sequence of
amino acids. Here, three of the four bases adenine,
guanine, cytosine and thymine (abbreviated
AGCT) in each case determines one amino acid,
e. g., UGG codes for tryptophan (cf. Fig. 1.12).
, (1.89)
Microvariants allow working in the picomole
range. In the reaction chamber, the protein
is fixed on a glass-fiber disc, and the coupling
and cleaving reagents are added and
removed in a carrier gas stream (vapour-phase
sequentiation).
Apart from the Edman degradation, other
methods can give valuable additional information
on sequence analysis. These methods
include the hydrolysis with amino- and carboxypeptidases
as mentioned in the case of
end group analysis and the fragmentation of
suitable volatile peptide derivatives in a mass
spectrometer.
Fig. 1.12. The genetic code