Step 
Action 
Product 
49 
Message 
A message molecule binds to 
a receptor and activates it. 
Each activated receptor 
activates many G proteins 
(two shown), which each 
activate one molecule of the 
enzyme adenylate cyclase. 
Using ATP. each molecule 
of adenylate cyclase make : 
many molecules of cyclic 
AMP. 
Receptor 
Cell membrane 
Activated 
adenylate 
cyclase 
G protein 
Cyclic AMP 
kinase. 
Each protein kinase 
molecule activates many 
cule 
of 
1 
A 
A 
* 
A 
A 
V 
V 
?in 
in 
m 
i ii 
in 
m 
/II 
m 
/ii 
/h 
in 
/i\ 
III 
M l 
1 1 1 
n i 
/ 1 1 
/ 1 \ 
/ 1 1 
I l V 
I l \ 
/ I I 
/ I i 
I l l 
/ I i 
/ l 1 
I It 
l l l 
I l I 
/ I l 
/ I I 
/ l l 
/ I \ 
/ I l 
/ I I 
/ I l 
l I I 
/ I l 
' I i 
i H! 
1 1 i 
1 1 \ 
;l I l 
I I l 
I I t 
/ I 1 
I I ' 
/ I \ 
I I \ 
I I t 
I I V 
I I 1 
I I 'V: 
I I ' 
I I 1 
I I 1 . 
/ I \ 
I I 1 
/ I 1 
/ I ' 
/ I l 
molecules of an enzyme 
Each copy oj the activated 
enzyme carries out its 
function. 
Activated 
protein kinase 
Activated enzyme 
Products of 
enzyme 
