Food Chemistry

46 1 Amino Acids, Peptides, Proteins

through second, third and subsequent repetitive
reactions:

, (1.89)

Microvariants allow working in the picomole
range. In the reaction chamber, the protein
is fixed on a glass-fiber disc, and the cou-
pling 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 infor-
mation on sequence analysis. These methods
include the hydrolysis with amino- and car-
boxypeptidases as mentioned in the case of
end group analysis and the fragmentation of
suitable volatile peptide derivatives in a mass
spectrometer.

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 increas-

ing 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 phos-

phoric 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. For-

mula 1.90). DNA is the carrier of the genetic

information which controls protein biosynthe-

sis 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 ade-

nine, guanine, cytosine and thymine (abbreviated

AGCT) in each case determines one amino acid,

e. g., UGG codes for tryptophan (cf. Fig. 1.12).

Fig. 1.12.The genetic code