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CAMPBELL

BIOLOGYReece • Urry • Cain • Wasserman • Minorsky • Jackson

© 2014 Pearson Education, Inc.

TENTH

EDITION

CAMPBELL

BIOLOGYReece • Urry • Cain • Wasserman • Minorsky • Jackson

TENTH

EDITION

11Cell

Communication

Lecture Presentation by

Nicole Tunbridge and

Kathleen Fitzpatrick


Cellular Messaging

Cells can signal to each other and interpret the

signals they receive from other cells and the

environment

Signals are most often chemicals

The same small set of cell signaling mechanisms

shows up in diverse species and processes


Figure 11.1


Figure 11.1a

Epinephrine


Concept 11.1: External signals are converted to responses within the cell

Communication among microorganisms provides

some insight into how cells send, receive, and

respond to signals


Evolution of Cell Signaling

The yeast, Saccharomyces cerevisiae, has two

mating types, a and

Cells of different mating types locate each other

via secreted factors specific to each type

Signal transduction pathways convert signals

received at a cell’s surface into cellular responses

The molecular details of signal transduction in

yeast and mammals are strikingly similar


Figure 11.2-1

Yeast cell,

mating type a

Exchange

of mating

factors

Receptor α factor

a factor Yeast cell,

mating type α

a α

1


Figure 11.2-2

Yeast cell,

mating type a

Exchange

of mating

factors

Receptor


mating type α

a α

1

a α

2 Mating

α factor


Figure 11.2-3

Yeast cell,

mating type a

Exchange

of mating

factors

Receptor


mating type α

a α

1

a α

2 Mating

3 New a/ cell

a/ α

α factor


Pathway similarities suggest that ancestral

signaling molecules that evolved in prokaryotes

and single-celled eukaryotes were adopted for use

in their multicellular descendants

Cell signaling is critical in the microbial world

A concentration of signaling molecules allows

bacteria to sense local population density in a

process called quorum sensing


Figure 11.3

Individual

rod-shaped

cells

1

3

2

2

0.5 mm

2.5 mm

Spore-forming

structure

(fruiting body)

Fruiting bodies

Aggregation

in progress


Figure 11.3a

Individual rod-shaped cells1

0.5 mm


Figure 11.3b

Aggregation in progress2

0.5 mm


Figure 11.3c

0.5 mm

Spore-forming structure

(fruiting body)

3


Figure 11.3d

2.5 mm

Fruiting bodies


Local and Long-Distance Signaling

Cells in a multicellular organism communicate via

signaling molecules

In local signaling, animal cells may communicate

by direct contact

Animal and plant cells have cell junctions that

directly connect the cytoplasm of adjacent cells

Signaling substances in the cytosol can pass

freely between adjacent cells


Figure 11.4Plasma membranes Cell wall

(a) Cell junctions

(b) Cell-cell recognition

Gap junctions

between animal cellsPlasmodesmata

between plant cells


In many other cases, animal cells communicate

using secreted messenger molecules that travel

only short distances

Growth factors, which stimulate nearby target cells

to grow and divide, are one class of such local

regulators in animals

This type of local signaling in animals is called

paracrine signaling


Synaptic signaling occurs in the animal nervous

system when a neurotransmitter is released in

response to an electric signal

Local signaling in plants is not well understood

beyond communication between plasmodesmata


In long-distance signaling, plants and animals use

chemicals called hormones

Hormonal signaling in animals is called endocrine

signaling; specialized cells release hormones,

which travel to target cells via the circulatory

system

The ability of a cell to respond to a signal depends

on whether or not it has a receptor specific to that

signal


Figure 11.5Local signaling

Target cells

Secreting

cell

Secretory

vesicles

Local regulator Target cell

(b) Synaptic signaling(a) Paracrine signaling

(c) Endocrine (hormonal) signaling

Electrical signal triggers

release of neurotransmitter.

Neurotransmitter

diffuses across

synapse.

Long-distance signaling

Endocrine cell Target cell

specifically

binds

hormone.

Hormone

travels in

bloodstream.

Blood

vessel


Figure 11.5a

Local signaling

Target cells

Secreting

cell

Secretory

vesicles

Local regulator

(a) Paracrine signaling


Figure 11.5b

Target cell

(b) Synaptic signaling

Electrical signal triggers

release of neurotransmitter.

Neurotransmitter

diffuses across

synapse.

Local signaling


Figure 11.5c

(c) Endocrine (hormonal) signaling

Long-distance signaling

Endocrine cell Target cell

specifically

binds

hormone.

Hormone

travels in

bloodstream.

Blood

vessel


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

Response


In reception, the target cell detects a signaling

molecule that binds to a receptor protein on the

cell surface

In transduction, the binding of the signaling

molecule alters the receptor and initiates a signal

transduction pathway; transduction often occurs

in a series of steps

In response, the transduced signal triggers a

specific response in the target cell


Figure 11.6-1

CYTOPLASM

Plasma membrane

EXTRACELLULAR

FLUID

Receptor

Signaling

molecule

Reception1


Figure 11.6-2

CYTOPLASM

Plasma membrane

EXTRACELLULAR

FLUID

Receptor

Signaling

molecule

Reception1 Transduction2

Relay molecules

1 2 3


Figure 11.6-3

CYTOPLASM

Plasma membrane

EXTRACELLULAR

FLUID

Receptor

Signaling

molecule

Reception1 Transduction2

Relay molecules

1 2 3

Response3

Activation

of cellular

response


Animation: Overview of Cell Signaling

Concept 11.3: Transduction: Cascades of molecular interactions relay signals from receptors to target molecules in the cell

Signal transduction usually involves multiple steps

Multistep pathways can greatly amplify a signal

Multistep pathways provide more opportunities for

coordination and regulation of the cellular

response



Signal Transduction Pathways

The binding of a signaling molecule to a receptor

triggers the first step in a chain of molecular

interactions

Like falling dominoes, the receptor activates

another protein, which activates another, and so

on, until the protein producing the response is

activated

At each step, the signal is transduced into a

different form, usually a shape change in a protein


Protein Phosphorylation and Dephosphorylation

Phosphorylation and dephosphorylation of

proteins is a widespread cellular mechanism for

regulating protein activity

Protein kinases transfer phosphates from ATP to

protein, a process called phosphorylation

Many relay molecules in signal transduction

pathways are protein kinases, creating a

phosphorylation cascade


Figure 11.10

Signaling molecule

Activated relay

moleculeReceptor

Inactive

protein kinase

1

Inactive

protein kinase

2

Inactive

protein kinase

3

Active

protein

kinase

1

Active

protein

kinase

2

Active

protein

kinase

3

Active

protein

Inactive

protein

ATP

ADP

PP

ATP

ADP

P i

P

P

P i

ATP

ADP

PP

PPP i

P

Cellular

response


Figure 11.10a

Signaling molecule

Activated relay

moleculeReceptor

Inactive

protein kinase

1 Active

protein

kinase

1


Figure 11.10b

Inactive

protein kinase

1

Inactive

protein kinase

2

Inactive

protein kinase

3

Active

protein

kinase

1

Active

protein

kinase

2

Active

protein

kinase

3

ATP

ADP

PPP

i

ATP

ADP

PPP

i

Phosphorylation

cascade

P

P


Figure 11.10c

Inactive

protein kinase

3 Active

protein

kinase

3

ATP

ADP

PPP

i

Pi

P

P

ATP

ADP

PP

Inactive

protein

Active

protein

Cellular

response


Protein phosphatases rapidly remove the

phosphates from proteins, a process called

dephosphorylation

This phosphorylation and dephosphorylation

system acts as a molecular switch, turning

activities on and off or up or down, as required


Small Molecules and Ions as Second Messengers

Many signaling pathways involve second

messengers

Second messengers are small, nonprotein,

water-soluble molecules or ions that spread

throughout a cell by diffusion

Second messengers participate in pathways

initiated by GPCRs and RTKs

Cyclic AMP and calcium ions are common second

messengers


Cyclic AMP

Cyclic AMP (cAMP) is one of the most widely

used second messengers

Adenylyl cyclase, an enzyme in the plasma

membrane, converts ATP to cAMP in response to

an extracellular signal


Figure 11.11

ATP cAMP AMP

PhosphodiesteraseAdenylyl cyclase

Pyrophosphate H2O


Figure 11.11a

ATP cAMP

Adenylyl cyclase

Pyrophosphate


Figure 11.11b

cAMP AMP

H2O

Phosphodiesterase


Many signal molecules trigger formation of cAMP

Other components of cAMP pathways are G

proteins, G protein-coupled receptors, and protein

kinases

cAMP usually activates protein kinase A, which

phosphorylates various other proteins

Further regulation of cell metabolism is provided

by G-protein systems that inhibit adenylyl cyclase


Figure 11.12

First messenger

(signaling molecule

such as epinephrine)

G protein

Adenylyl

cyclase

G protein-coupled

receptorSecond

messenger

Cellular responses

Protein

kinase A

GTP

ATP

cAMP


Understanding of the role of cAMP in G protein

signaling pathways helps explain how certain

microbes cause disease

The cholera bacterium, Vibrio cholerae, produces

a toxin that modifies a G protein so that it is stuck

in its active form

This modified G protein continually makes cAMP,

causing intestinal cells to secrete large amounts of

salt into the intestines

Water follows by osmosis and an untreated person

can soon die from loss of water and salt


Calcium Ions and Inositol Triphosphate (IP3)

Calcium ions (Ca2+) act as a second messenger in

many pathways

Ca2+ can function as a second messenger

because its concentration in the cytosol is

normally much lower than the concentration

outside the cell

A small change in number of calcium ions thus

represents a relatively large percentage change in

calcium concentration


Figure 11.13

Endoplasmic

reticulum (ER)Plasma

membrane

Mitochondrion

ATP

ATP

ATPCYTOSOL

Nucleus

Ca2+

pump

EXTRACELLULAR

FLUID

Key High [Ca2+] Low [Ca2+]


A signal relayed by a signal transduction pathway

may trigger an increase in calcium in the cytosol

Pathways leading to the release of calcium involve

inositol triphosphate (IP3) and diacylglycerol

(DAG) as additional second messengers

These two are produced by cleavage of a certain

phospholipid in the plasma membrane


Figure 11.14-1

EXTRA-

CELLULAR

FLUID

Signaling molecule

(first messenger)

G protein

GTP

CYTOSOLG protein-coupled

receptor Phospholipase C

DAG

PIP2

IP3

(second messenger)

IP3-gated

calcium channel

Ca2+

Nucleus

Endoplasmic

reticulum (ER)

lumen


Figure 11.14-2

EXTRA-

CELLULAR

FLUID

Signaling molecule

(first messenger)

G protein

GTP



DAG

PIP2

IP3

(second messenger)

IP3-gated

calcium channel

Ca2+

Nucleus

Endoplasmic

reticulum (ER)

lumen

Ca2+

(second

messenger)


Figure 11.14-3

EXTRA-

CELLULAR

FLUID

Signaling molecule

(first messenger)

G protein

GTP



DAG

PIP2

IP3

(second messenger)

IP3-gated

calcium channel

Ca2+

Nucleus

Endoplasmic

reticulum (ER)

lumen

Ca2+

(second

messenger)

Various

proteins

activated

Cellular

responses


Animation: Signal Transduction Pathways

Concept 11.4: Response: Cell signaling leads to regulation of transcription or cytoplasmic activities

The cell’s response to an extracellular signal is

called the “output response”



Nuclear and Cytoplasmic Responses

Ultimately, a signal transduction pathway leads to

regulation of one or more cellular activities

The response may occur in the cytoplasm or in the

nucleus

Many signaling pathways regulate the synthesis of

enzymes or other proteins, usually by turning

genes on or off in the nucleus

The final activated molecule in the signaling

pathway may function as a transcription factor


Figure 11.15

Growth factor

Receptor

Phospho-rylation

cascade

Reception

Transduction

CYTOPLASM

Inactive

transcription

factor

Activetranscriptionfactor

DNA

ResponseP

Gene

mRNANUCLEUS


Figure 11.15a

Growth factor

Receptor

Phospho-rylation

cascade

Reception

Transduction

NUCLEUS

CYTOPLASM

Inactive

transcription

factor


Figure 11.15b

NUCLEUS

CYTOPLASM

Phospho-rylation

cascade Transduction

Inactive

transcription

factor

Active

transcription

factor Response

DNA

P

Gene

mRNA


Other pathways regulate the activity of enzymes

rather than their synthesis

For example, a signal could cause opening or

closing of an ion channel in the plasma

membrane, or a change in cell metabolism


Figure 11.16

Reception Transduction

Inactive

G protein

Active G protein (102 molecules)

Inactive

adenylyl cyclase

Active adenylyl cyclase (102)

ATP

Cyclic AMP (104)

Inactive

protein kinase A

Active protein kinase A (104)

Inactive

phosphorylase kinase

Active phosphorylase kinase (105)

Active glycogen phosphorylase (106)

Inactive

glycogen phosphorylaseGlycogen

Response

Glucose 1-phosphate

(108 molecules)

Binding of epinephrine to G protein-coupled

receptor

(1 molecule)


Figure 11.16a

Reception

Glycogen

Response

Glucose 1-phosphate

(108 molecules)

Binding of epinephrine to G protein-coupled

receptor

(1 molecule)


Figure 11.16b

Transduction

Inactive

G protein

Active G protein (102 molecules)

Inactive

adenylyl cyclase

Active adenylyl cyclase (102)

ATP

Cyclic AMP (104)

Inactive

protein kinase A



Figure 11.16c

Inactive

phosphorylase kinase

Active phosphorylase kinase (105)

Active glycogen phosphorylase (106)

Inactive

glycogen phosphorylase

Cyclic AMP (104)

Inactive

protein kinase A


Transduction


Signaling pathways can also affect the overall

behavior of a cell, for example, a signal could lead

to cell division


Regulation of the Response

A response to a signal may not be simply “on” or

“off”

There are four aspects of signal regulation to

consider

Amplification of the signal (and thus the response)

Specificity of the response

Overall efficiency of response, enhanced by

scaffolding proteins

Termination of the signal


Signal Amplification

Enzyme cascades amplify the cell’s response to

the signal

At each step, the number of activated products is

much greater than in the preceding step


The Specificity of Cell Signaling and Coordination of the Response

Different kinds of cells have different collections of

proteins

These different proteins allow cells to detect and

respond to different signals

The same signal can have different effects in cells

with different proteins and pathways

Pathway branching and “cross-talk” further help

the cell coordinate incoming signals


Figure 11.17

Signaling

molecule

Receptor

Relay

mole-

cules

Response 1 Response 2 Response 3 Response 4 Response 5

Cell A: Pathway leads

to a single response.

Cell B: Pathway

branches, leading to

two responses.

Cell C: Cross-talk

occurs between two

pathways.

Cell D: Different

receptor leads to a

different response.

Activation

or inhibition


Figure 11.17a

Signaling

molecule

Receptor

Relay

mole-

cules

Response 1 Response 2 Response 3

Cell A: Pathway leads

to a single response.

Cell B: Pathway

branches, leading to

two responses.


Figure 11.17b

Response 4 Response 5

Cell C: Cross-talk

occurs between two

pathways.

Cell D: Different

receptor leads to a

different response.

Activation

or inhibition


Signaling Efficiency: Scaffolding Proteins and Signaling Complexes

Scaffolding proteins are large relay proteins to

which other relay proteins are attached

Scaffolding proteins can increase the signal

transduction efficiency by grouping together

different proteins involved in the same pathway

In some cases, scaffolding proteins may also help

activate some of the relay proteins


Figure 11.18

Signaling

molecule

Receptor

Scaffolding

protein

Plasma

membrane

Three

different

protein

kinases


Termination of the Signal

Inactivation mechanisms are an essential aspect

of cell signaling

If ligand concentration falls, fewer receptors will be

bound

Unbound receptors revert to an inactive state

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