Biology Reference
In-Depth Information
specific signals
A
B
C
part common to the three
signalling pathways
A'
B'
C'
specific responses
F
IGURE
9. The problem of the specificity of the signal.
Three signals A, B and C
activate three responses in a cell, A
respectively. Yet they use in part
a single signalling pathway. How is the specificity of these signals maintained?
′
, B
′
and C
′
We could easily generalise these examples and show that the
same question arises for the regulation of gene expression. How
can genetic programming work if the interactions between the reg-
ulator proteins and their target sequences in the DNA are not
specific?
Systematic study of proteomes has shown that all the signalling
pathways of a cell are interconnected (see this chapter, §4.1.4).
When the molecular complexes of a cell are isolated and analysed,
at least 37% of the proteins are found in several complexes per-
forming different functions (Krause
et al
., 2004). This is therefore a
general problem in the way cell networks function. How can a par-
ticular signal induce a specific response instead of activating all the
functions of the cell and causing all the effects possible to be scram-
bled? How does the cell function in these conditions? It is usually
suggested that the functioning of molecular networks is itself
subject to spatial and temporal dynamics, and therefore the same
parts of a network would not be activated at the same time at a
