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Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

PowerPoint Lectures for

Biology, Seventh Edition

Neil Campbell and Jane Reece

Lectures by Chris Romero

Chapter 11

Cell Communication


Overview: The Cellular Internet

• Cell-to-cell communication is essential for multicellular organisms

• Biologists have discovered some universal mechanisms of cellular regulation

• Signals may originate from

other cells or from physical

changes in the

environment.

– Environmental changes

may include light and touch


Evolution of Cell Signaling

• 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

• Signal transduction pathways convert signals on a cell’s surface into cellular responses

• Pathway similarities suggest that ancestral signaling molecules evolved in prokaryotes and have since been adopted by eukaryotes

LE 11-2

a a

a a

a/a

Exchange of

mating factors

Mating

Receptor a factor

a factorYeast cell,

mating type a

Yeast cell,

mating type a

New a/a cell


Local and Long-Distance Signaling

• Cells in a multicellular organisms

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

• In many other cases, animal cells communicate

using local regulators, messenger molecules that

travel only short distances

LE 11-3Plasma membranes

Gap junctions

between animal cells

Cell junctions

Cell-cell recognition

Plasmodesmata

between plant cells


Types of Signaling

• Paracrine signaling involves local regulators

– Released into extracellular fluid

– Example: growth factors

• Synaptic signaling occurs in animal nervous system.

– More targeted than Paracrine

– An electrical signal causes release of a chemical

signal which diffuses across the synapse between

nerve cells.

• Local signals are different in plants due to cell wall

• In long-distance signaling, plants and animals use

chemicals called hormones

LE 11-4

Paracrine signaling

Local regulator

diffuses through

extracellular fluid

Secretory

vesicle

Secreting

cell

Target cell

Local signaling

Electrical signal

along nerve cell

triggers release of

neurotransmitter

Neurotransmitter

diffuses across

synapse

Endocrine cell Blood

vessel

Long-distance signaling

Hormone travels

in bloodstream

to target cells

Synaptic signaling

Target cell

is stimulated

Hormonal signaling

Target

cell


STAGES OF CELL SIGNALING

• Reception

• Transduction

• Response


Figure 11.6-1

Plasma membrane

EXTRACELLULAR

FLUIDCYTOPLASM

Reception

Receptor

Signaling

molecule

1


Figure 11.6-2

Plasma membrane

EXTRACELLULAR

FLUIDCYTOPLASM

Reception Transduction

Receptor

Signaling

molecule

Relay molecules in a signal transduction

pathway

21


Figure 11.6-3

Plasma membrane

EXTRACELLULAR

FLUIDCYTOPLASM

Reception Transduction Response

Receptor

Signaling

molecule

Activation

of cellular

responseRelay molecules in a signal transduction

pathway

321


Reception: A signal molecule binds to a receptor protein, causing it to change shape

• The binding between a signal molecule (ligand)

and receptor is highly specific

• A conformational change in a receptor is often

the initial transduction of the signal

• Most signal receptors are plasma membrane

proteins

– Examples: G-protein-linked receptors

– Some receptor proteins are intracellular,

found in the cytosol or nucleus of target cells

LE 11-6

EXTRACELLULAR

FLUID

Plasma

membrane

The steroid

hormone testosterone

passes through the

plasma membrane.

Testosterone binds

to a receptor protein

in the cytoplasm,

activating it.

The hormone-

receptor complex

enters the nucleus

and binds to specific

genes.

The bound protein

stimulates the

transcription of

the gene into mRNA.

The mRNA is

translated into a

specific protein.CYTOPLASM

NUCLEUS

DNA

Hormone

(testosterone)

Receptor

protein

Hormone-

receptor

complex

mRNA

New protein


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

• Transduction usually involves multiple steps

• Multistep pathways can amplify a signal: A few molecules can produce a large cellular response

• Multistep pathways provide more opportunities for coordination and regulation

http://highered.mcgraw-hill.com/olcweb/cgi/pluginpop.cgi?it=swf::535::535::/sites/dl/free/0072437316/120069/bio08.swf::Signal%20Amplification


Signal Transduction Pathways

• The molecules that relay a signal from receptor to response are mostly proteins

• 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 conformational change


Phosphorylation Cascade

• In many pathways, the signal is transmitted by a cascade of protein phosphorylations

• Phosphatase enzymes remove the phosphates

• This phosphorylation and dephosphorylationsystem acts as a molecular switch, turning

activities on and off

• Kinase: an enzyme that phosphorylates other enzymes

LE 11-8

Signal molecule

Activated relay

molecule

Receptor

Inactive

protein kinase

1 Active

protein

kinase

1

Inactive

protein kinase

2 Active

protein

kinase

2

Inactive

protein kinase

3 Active

protein

kinase

3

ADP

Inactive

protein

Active

protein

Cellular

response

ATP

PPP i

ADPATP

PPP i

ADPATP

PPP i

P

P

P


G-Protein Linked Receptor

• G-Protein Linked Receptor: membrane bound receptor often used in signal transduction pathways

– Works with a G-protein

– G-protein is like an on/off switch

• When GDP is bound to the G-protein it is inactive

• GTP bound to the G-protein makes it active


Figure 11.7b

G protein-coupled

receptor

21

3 4

Plasmamembrane

G protein(inactive)

CYTOPLASMEnzyme

Activatedreceptor

Signalingmolecule

Inactiveenzyme

Activatedenzyme

Cellular response

GDPGTP

GDPGTP

GTP

P i

GDP

GDP


Second Messengers

• Second messengers are small, nonprotein, water-

soluble molecules or ions

– Involved in transduction

– Examples: Cyclic AMP (cAMP) and Calcium

• cAMP is created from ATP by the membrane

bound enzyme adenylyl cyclase

• The extracellular signal molecule that binds to the

membrane is a pathway’s “first messenger”

• Second messengers can readily spread

throughout cells by diffusion

LE 11-10

cAMP

ATPSecond

messenger

First messenger

(signal molecule

such as epinephrine)

G-protein-linked

receptor

G protein

Adenylyl

cyclase

Protein

kinase A

Cellular responses

GTP


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

• The cell’s response to an extracellular signal is sometimes called the “output response”

• What is the final step?

• Ultimately, a signal transduction pathway leads to regulation of one or more cellular activities

– The response may occur in the cytoplasm or may involve action in the nucleus

– Many pathways regulate the activity or synthesis of enzymes

– May turn on and off genes

LE 11-14

ReceptionGrowth factor

Receptor

Phosphorylation

cascade

Transduction

CYTOPLASM

Inactive

transcription

factor

Active

transcription

factorP

Response

Gene

mRNA

DNA

NUCLEUS


Glucose Homeostasis

https://www.youtube.com/watch?v=tN78hYn3ehc

https://www.youtube.com/watch?v=tN78hYn3ehc


Glucose Homeostasis

• What does your Pancreas do?

• Insulin and Regulation of Glucose in Blood

• Signal Transduction Animation

• Breakdown of Glycogen

https://www.youtube.com/watch?v=8dgoeYPoE-0

https://www.youtube.com/watch?v=OlHez8gwMgw

https://www.youtube.com/watch?v=FtVb7r8aHco

https://www.youtube.com/watch?v=oBL0OC3IavI


Signal Transduction Modeling

• Create a model that demonstrate signal transduction.

• The protein hormone glucagon that binds to a receptor in

the plasma membrane with a cytoplasmic response

through a G-protein & 2nd messenger & phosphorylation

cascade (that leads to the breakdown glycogen to

glucose).

• Must Include: G-protein linked receptor, G protein,

Adenylyl Cyclase, ATP & cAMP, multiple kinases,

phosphates, glycogen phosphorylase, glycogen (&

glucose)

• Note: The final response is carried out by the

phosphorylation the enzyme glycogen phosphorylase


Fine-Tuning of the Response

• Multistep pathways have two important benefits:

– Amplifying the signal (and thus the response)

• Enzyme cascades amplify the cell’s

response

• At each step, the number of activated

products is much greater than in the

preceding step

– Contributing to the specificity of the response


The Specificity of Cell Signaling

• Different kinds of cells have different collections of proteins

• These differences in proteins give each kind of cell specificity in detecting and responding to signals

• The response of a cell to a signal depends on

the cell’s particular collection of proteins

• Pathway branching and “cross-talk” further help the cell coordinate incoming signals

LE 11-15Signal

molecule

Receptor

Relay

molecules

Response 1 Response 2 Response 3

Cell B. Pathway branches,

leading to two responses

Cell A. Pathway leads

to a single response

Cell C. Cross-talk occurs

between two pathways

Response 4 Response 5

Activation

or inhibition

Cell D. Different receptor

leads to a different response


Termination of the Signal

• Inactivation mechanisms are an essential aspect of cell signaling

• When signal molecules leave the receptor, the receptor reverts to its inactive state


Polar and Non-polar Hormones

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