11.1 External signals are
converted to responses
within the cell
Cell Communication
https://www.youtube.com/watch?v=TVfmUfr8VPA
Evolution of Cell Signaling: S.
cerevisiae
 The yeast, S. cerevisiae, has two mating
types, a and .
 Cells of different mating types locate each
other via secreted factors specific to each
type.
 Each type secretes a specific factor that binds to
receptors only on the other type of cell.
 When exposed to each other’s mating factors, a
pair of opposite cell types fuse (mate).
Figure 11.2
 factor
Receptor
 Once received by
1 Exchange
of mating
factors
the yeast cell surface
a

receptor, a mating
Each cell
signal is changed, or
type secretes
a mating
transduced, into a
factor that
a factor
form that brings
Yeast
cell,
Yeast cell,
binds to
mating type 
receptors on mating type a
about the cellular
the other cell
response of mating.
type.
2 Mating
 A signal transduction
Binding of the
factors to
pathway is a series of
a

receptors
steps by which a
induces
changes in
signal on a cell’s
cells that
surface is converted
leads to their
fusion.
into a specific
3 New a/ cell
cellular response.
a/
Local and LongDistance
Signaling
 Cells in a multicellular
organism
communicate by
chemical messengers.
 Animal and plant cells
have cell junctions
that directly connect
the cytoplasm of
adjacent cells.
 In local signaling, animal cells may communicate by
direct contact, or cell-cell recognition.
In many other cases, animal cells communicate
using local regulators, messenger molecules that
travel only short distances.
Long-distance signaling
Endocrine cell
Blood
vessel
Hormone travels
in bloodstream.
Target cell
specifically
binds
hormone.
(c) Endocrine (hormonal) signaling
 In long-distance
signaling, plants and
animals use
chemicals called
hormones.
 The ability of a cell
to respond to a
signal depends on
whether or not it has
a receptor specific
to that signal.
The Three Stages of Cell
Signaling: A Preview
 Earl W. Sutherland discovered how the
hormone epinephrine acts on cells.
 Sutherland suggested that cells receiving
signals went through three processes: reception,
transduction, and response.