Chemistry Reference
In-Depth Information
Figure 5.7 Stochastic model of transmembrane
signaling by chemoattractant receptors. (A) Signal
transduction reactions by chemoattractant
receptors. The ligand (L) binds to the inactive
receptor (R) leading to the formation of an active
receptor (R
), which produces the active second
messenger (X
) from the inactive precursor (X).
The active X
is switched off to the inactive state X
in due time. (B) The cell is placed under a ligand
concentration gradient, which leads to variations
in the concentration of the second messenger
between the anterior and posterior ends of the
cell. See text for details. (C) Dependence of
the SNR of chemotactic signals on ligand
concentration obtained theoretically using
Equation 5.5. Parameter values used for the
calculation are summarized in our previous
report [25]. The theoretically-obtained SNR
(red line) was overlaid on the experimental
data to verify the chemotactic accuracy of
Dictyostelium cells (green circles) as reported by
Fisher et al.[16].
X
total
is the total number of second messenger molecules per cell, K
X
ΒΌ
k
d
/k
p
is the
concentration of active receptors where the activation of the second messenger
reaches half-maximum with production and degradation rates of k
p
and k
d
for the
second messenger. Note that Equation 5.2 represents the input
-
output relationship
between the average number of active receptors and the average number of active
second messengers. To describe the signal and noise propagation during transmem-
brane signaling by the receptors, the input
-
output relationship between temporal
noise in the concentration of the active receptor (
2
R
) and noise in the concentration of
s
2
X
) should be taken into account.
the active second messenger (
s
