
6 Feedback Control in Systems Biology
C
1
C
2
C
3
P
1
P
2
P
3
Tryptophan
-
-
-
+
+
FIGURE 1.5: Tryptopha n operon regula tory sy stem in E. coli viewed as a dis-
tributed feedback control system: tryptophan is the product of three processes
in series, namely transcription P
1
, translation P
2
and tryptophan synthesis
P
3
, controlled by three distinct negative feedback controllers, namely genetic
regulation C
1
, mRNA attenuation C
2
and enzyme inhibition C
3
.
1.2.2 The polyamine feedback control system
Polyamines are esse ntial, ubiquitous polycations found in all eukaryotic and
most prokaryotic cells. They are utilised in a wide range of core cellular
processes such as binding ...