Essential Cell Biology 5th edition

538 CHAPTER 16 Cell Signaling
(A) heart pacemaker cell
(B) salivary gland cell
(C) skeletal muscle cell
(D) acetylcholine
acetylcholine
O
receptor
protein
H 3 C
C
CH 3
O CH 2 CH 2 N + CH 3
CH 3
DECREASED RATE
OF FIRING
SECRETION
CONTRACTION
Figure 16–5 The same signal molecule
can induce different responses in
different target cells. Different cell
types are configured to respond to the
neurotransmitter acetylcholine in different
ways. Acetylcholine binds to similar receptor
proteins on (A) heart pacemaker cells
and (B) salivary gland cells, but it evokes
different responses in each cell type.
(C) Skeletal muscle cells produce a different
type of receptor protein for the same signal
molecule. (D) For such a versatile molecule,
acetylcholine has a fairly simple chemical
structure.
a relatively small number of signal molecules, used in different combinations,
to exert subtle and complex control over cell behavior. A
combination of signals can evoke a response that is different from the
sum of the effects that each signal would trigger on its own. As we discuss
later, this “tailoring” of a cell’s response occurs, in part, because
the intracellular relay systems activated by the different signals interact.
Thus the presence of one signal will often modify the effects of another.
One combination of signals might enable a cell to survive; another might
drive it to differentiate in some specialized way; and another might cause
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it to divide. In the absence of the proper signals, most animal cells are
programmed to kill themselves (Figure 16–6).
A Cell’s Response to a Signal Can Be Fast or Slow
The length of time a cell takes to respond to an extracellular signal can
vary greatly, depending on what needs to happen once the message has
A
B
SURVIVE
C
A
B
GROW + DIVIDE
Figure 16–6 An animal cell depends on
multiple extracellular signals. Every cell
type displays a set of receptor proteins that
enables it to respond to a specific set of
extracellular signal molecules produced by
other cells. These signal molecules work in
combinations to regulate the behavior of
the cell. As shown here, cells may require
multiple signals (blue arrows) to survive,
additional signals (red arrows) to grow and
divide, and still other signals (green arrows)
to differentiate. If deprived of the necessary
survival signals, most cells undergo a
form of cell suicide known as apoptosis
(discussed in Chapter 18).
C
A
B
C
D
F
E
G
DIFFERENTIATE
DIE
apoptotic
cell