Control of Cells by Chemical Messengers
129
Figure 5–8
Example of signal amplifi cation. In this example, a
single molecule of a fi rst messenger results in 1 million
fi nal products. Other second-messenger pathways have
similar amplifi cation processes.
Figure 5–8
physiological
inquiry
What are the advantages of having an enzyme like
adenylyl cyclase involved in the initial response to
receptor activation by a fi rst messenger?
Answer can be found at end of chapter.
cAMP
(each kinase phosphorylates enzymes)
(each enzyme activates100 final products)
Phosphorylated enzyme
Receptor
First
messenger
cAMP-dependent protein kinase
Protein
kinase
Protein
kinase
Protein
kinase
Protein
kinase
Enzyme
Enzyme
Enzyme
Enzyme
Number of molecules
Phosphorylated enzyme
1
100
100
10,000
1,000,000
Ion
channel
lum
cul
tic
ret
c re
mic
las
opla
dop
End
En
Nucleus
Plasma
membrane
A
D
ADP
DP
A
TP
ATP
M
i
c
icr
cro
cro
rot
otu
otu
tub
ub
ubu
bu
bule
ule
ules
les
es
e
Active
transport
s
si
es
th
nt
syn
s
in
tein
ote
Pro
P
a
Ca
C
2+
2
rt
or
po
sp
an
ra
tr
S
e
Se
Sec
ecr
ecr
cre
cre
ret
etio
etio
tion
ion
on
on
Glycogen
breakdown
Lipid
breakdown
DNA
synthesis
RNA
synthesis
nt
nt
n
en
e
de
d
nd
nd
en
pen
depe
c
A
cA
M
P
MP-
MP-depe
MP-dep
P-dep
P-de
Pd
protein kinase
protein kinase
protein kinase
protein kinase
protein kinase
protein kinas
protein kina
rotein kin
rotein ki
otein k
Enzyme 1
Enzyme 1
Enzyme 1
Enzyme 1
Enzyme
Enzyme
Enzyme
Enzyme
Enzyme
nzym
nzym
nzym
nzym
nzym
2
Enzyme 2
Enzyme 2
Enzyme
Enzyme
Enzyme
Enzyme
Enzyme
Enzyme
Enzym
nzym
nzym
nzym
nzym
Figure 5–9
The variety of cellular responses induced by cAMP is due mainly
to the fact that activated cAMP-dependent protein kinase can
phosphorylate many different proteins, activating or inhibiting
them. In this fi gure, the protein kinase is shown phosphorylating
seven different proteins—a microtubular protein, an ATPase, an ion
channel, a protein in the endoplasmic reticulum, a protein involved
in DNA synthesis, and two enzymes.
Figure 5–9
physiological
inquiry
Does a given protein kinase, such as cAMP-dependent protein
kinase, phosphorylate the same proteins in all cells in which the
kinase is present?
Answer can be found at end of chapter.
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