AP Biology

Chapter 11Cell Communication

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Gap junctionsbetween animal cells

Cell-Cell Communication

Animal cells use gap junctions to send signals Cells must be in direct contact Protein channels connecting two

adjoining cells

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Cell-Cell Communication

Plasmodesmata between plant cells

Plant cells use plasmodesmata to send signals Cells must be in direct contact Gaps in the cell wall connecting the two

adjoining cells together

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Local Signaling Other types of signaling over a short

distance Cell-cell recognition

Membrane bound cell surface molecules Glycoproteins Glyolipids

Local regulators Growth factors Only work over a short distance

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Long-Distance Signaling Nervous System in Animals

Electrical signals through neurons

Endocrine System in Animals Uses hormones to transmit messages

over long distances

Plants also use hormones Some transported through vascular

system Others are released into the air

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Reception1

EXTRACELLULARFLUID

Receptor

Signalingmolecule

Plasma membrane

CYTOPLASM

1

Three Stages of Cell Signaling

Signaling molecule binds to the receptor protein

The receptor and signaling molecules fit together (lock and key model, induced fit model, just like enzymes!)

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Three Stages of Cell Signaling

Reception1

EXTRACELLULARFLUID

Receptor

Signalingmolecule

Plasma membrane

CYTOPLASM

1

Relay molecules in a signal transduction pathway

Transduction2

The signal is converted into a form that can produce a cellular response

2nd Messenger!

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EXTRACELLULARFLUID

Plasma membrane

CYTOPLASM

Receptor

Signalingmolecule

Relay molecules in a signal transduction pathway

Activationof cellularresponse

Reception Transduction Response1 2 3

Three Stages of Cell Signaling

The transduced signal triggers a cellular response

Can be catalysis, activation of a gene, triggering apoptosis, almost anything!

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G protein-coupledreceptor

Plasmamembrane

Enzyme

G protein(inactive)

GDP

CYTOPLASM

Activatedenzyme

GTP

Cellular response

GDP

P

i

Activatedreceptor

GDP GTP

Signaling molecule

Inactiveenzyme

1 2

3 4

G-Protein Receptors

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Signalingmolecule(ligand)

Gateclosed Ions

Ligand-gatedion channel receptor

Plasmamembrane

Gate open

Cellularresponse

Gate closed

1

2

3

Ion Channel Receptors Very important in

the nervous system Signal triggers the

opening of an ion channel depolarization Triggered by

neurotransmitters

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Fig. 11-9

Signaling molecule

ReceptorActivated relaymolecule

Inactiveprotein kinase

1 Activeproteinkinase

1

Inactiveprotein kinase

2

ATPADP Active

proteinkinase

2

P

PPP

Inactiveprotein kinase

3

ATPADP Active

proteinkinase

3

P

PPP

i

ATPADP P

ActiveproteinPP

P i

Inactiveprotein

Cellularresponse

Phosphorylation cascadei

Transduction:A Phosphorylation

Cascade

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First messengerFig. 11-11

G protein

Adenylylcyclase

GTP

ATP

cAMPSecondmessenger

Proteinkinase A

G protein-coupledreceptor

Cellular responses

Transduction in a G-protein pathway

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Response Many possible

outcomes This example

shows a transcription response

Growth factor

Receptor

Phosphorylationcascade

Reception

Transduction

Activetranscriptionfactor Response

P

Inactivetranscriptionfactor

CYTOPLASM

DNA

NUCLEUSmRNA

Gene

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Specificity of the signal The same signal

molecule can trigger different responses

Many responses can come from one signal!

Signalingmolecule

Receptor

Relaymolecules

Response 1

Cell A. Pathway leadsto a single response.

Cell B. Pathway branches,leading to two responses.

Response 2 Response 3

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The signal can also trigger an activator or inhibitor

The signal can also trigger multiple receptors and different responses Response 4 Response 5

Activationor inhibition

Cell C. Cross-talk occursbetween two pathways.

Cell D. Different receptorleads to a different response.

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