1. 11.1 External signals are converted to responses within the cell
Cell Communication

2. 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).

3. Figure 11.2
 factor
Receptor
Once received by the yeast cell surface receptor, a mating signal is changed, or transduced, into a form that brings about the cellular response of mating.
A signal transduction pathway is a series of steps by which a signal on a cell’s surface is converted into a specific cellular response. 1
Exchange of mating factors a 
Each cell type secretes a mating factor that binds to receptors on the other cell type.
a factor
Yeast cell,
mating type a
Yeast cell,
mating type  2
Mating
Binding of the factors to receptors induces changes in cells that leads to their fusion. a 
Figure 11.2 Communication between mating yeast cells. 3
New a/ cell
a/

4. Local and Long-Distance 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.

5. In many other cases, animal cells communicate using local regulators, messenger molecules that travel only short distances.

6. Long-distance signaling
Endocrine cell
Blood vessel
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.
Hormone travels in bloodstream.
Target cell specifically binds hormone.
(c) Endocrine (hormonal) signaling

7. 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.
Sutherland and his colleagues at Vanderbilt University were investigating how the animal hormone epinephrine stimulates the breakdown of the storage polysaccharide glycogen within liver cells and skeletal muscles.
The effect of epinephrine is the mobilization of fuel reserves.
Glycogen is broken down into glucose (which goes to the bloodstream) or an early intermediate of glycolysis.
Experiment
Epinephrine added to test tube with glycogen and glycogen phosphorylase results in no glycogen breakdown.
Glycogen phosphorylase could be activated by epinephrine only then the hormone was added to intact cells in a solution.
Conclusion
Epinephrine does not interact directly with the enzyme responsible for glycogen breakdown.
The plasma membrane itself is necessary for transmission of the signal to take place.