Cell CommunicationChapter 11

Cellular MessagingCell-to-cell communication is

essential for both multicellular and unicellular organisms.

Cells can signal to each other and interpret the signals they receive from other cells and the environment.Signals include light, touch, and

chemicals.Biologists have discovered some

universal mechanisms of cellular regulation.The same small set of cell-

signaling mechanisms shows up again and again in diverse species.

The fight-or-flight response is triggered by a signaling molecule called epinephrine

11.1 External signals are converted to responses within the cell

Evolution of Cell Signaling: S. cerevisiaeThe yeast, Saccharomyces 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).Offspring contains a combination of genetic material that

is advantageous.

Figure 11.2

Exchange of mating factors

Receptor factor

a factorYeast cell,mating type a

Yeast cell,mating type

Mating

New a/ cell

1

2

3

a

a

a/

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.

Each cell type secretes a mating factor that binds to receptors on the other cell type.Binding of the factors to receptors induces changes in cells that leads to their fusion.

Evolution of Cell Signaling: BacteriaBacterial cells secrete molecules that can be detected

by other bacterial cells.Sensing the concentration of such signaling molecules

allows bacteria to monitor the local density of cells, called quorum sensing.

Quorum sensing allows bacterial populations to coordinate their behaviors in activities that require a given number of cells acting simultaneously.Example: biofilm formation.

Local and Long-Distance SignalingCells 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.

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.

Long-distance signaling

Endocrine cell Bloodvessel

Hormone travelsin bloodstream.

Target cellspecificallybinds hormone.

(c) Endocrine (hormonal) signaling

The Three Stages of Cell Signaling: A PreviewEarl W. Sutherland discovered how the

hormone epinephrine acts on cells.Sutherland suggested that cells receiving

signals went through three processes:ReceptionTransductionResponse

Plasma membrane

EXTRACELLULARFLUID

CYTOPLASM

Reception Transduction Response

Receptor

Signalingmolecule

Activationof cellularresponse

Relay molecules in a signal transductionpathway

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Concept Check1. Explain how signaling is involved in

ensuring that yeast cells fuse only with cells of the opposite mating type.

2. In liver cells, glycogen phosphorylase acts in which of the three stages of the signaling pathway associated with an epinephrine-initiated signal?