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Chapter 11 Cell Communication
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Overview: The Cellular Internet
Cell-to-cell communication is essential for multicellular organisms Biologists have discovered some universal mechanisms of cellular regulation The combined effects of multiple signals determine cell response For example, the dilation of blood vessels is controlled by multiple molecules Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
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Fig. 11-1 Figure 11.1 How do the effects of Viagra (multicolored) result from its inhibition of a signaling-pathway enzyme (purple)?
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Concept 11.1: External signals are converted to responses within the cell
Microbes: are a window on the role of cell signaling in the evolution of life Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
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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 Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
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Yeast cell, mating type a Yeast cell, mating type
Fig. 11-2 factor Receptor 1 Exchange of mating factors a a factor Yeast cell, mating type a Yeast cell, mating type 2 Mating a Figure 11.2 Communication between mating yeast cells New a/ cell a/ 3
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Pathway similarities suggest that:
Ancestral signaling molecules: Evolved in prokaryotes Modified later in eukaryotes Signaling molecules concentration in bacteria: Allow them to detect population density Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
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1 Individual rod- shaped cells 2 Aggregation in process 3
Fig. 11-3 1 Individual rod- shaped cells 2 Aggregation in process 0.5 mm 3 Spore-forming structure (fruiting body) Figure 11.3 Communication among bacteria Fruiting bodies
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Local and Long-Distance Signaling
Cellular communication can be by: Chemical messengers Direct cytoplasmic connection thru: Cell junctions of adjacent cells Direct contact, or cell-cell recognition Short distance communication uses: Local messenger molecules for Long distance communication uses: Hormones for -distance signaling Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
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Gap junctions between animal cells Plasmodesmata between plant cells
Fig. 11-4 Plasma membranes Gap junctions between animal cells Plasmodesmata between plant cells (a) Cell junctions Figure 11.4 Communication by direct contact between cells (b) Cell-cell recognition
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Figure 11.5 Local and long-distance cell communication in animals
Local signaling Long-distance signaling Target cell Electrical signal along nerve cell triggers release of neurotransmitter Endocrine cell Blood vessel Neurotransmitter diffuses across synapse Secreting cell Secretory vesicle Hormone travels in bloodstream to target cells Local regulator diffuses through extracellular fluid Target cell is stimulated Target cell Figure 11.5 Local and long-distance cell communication in animals (a) Paracrine signaling (b) Synaptic signaling (c) Hormonal signaling
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(a) Paracrine signaling (b) Synaptic signaling
Fig. 11-5ab Local signaling Target cell Electrical signal along nerve cell triggers release of neurotransmitter Neurotransmitter diffuses across synapse Secreting cell Secretory vesicle Figure 11.5 Local and long-distance cell communication in animals Local regulator diffuses through extracellular fluid Target cell is stimulated (a) Paracrine signaling (b) Synaptic signaling
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Long-distance signaling
Fig. 11-5c Long-distance signaling Endocrine cell Blood vessel Hormone travels in bloodstream to target cells Figure 11.5 Local and long-distance cell communication in animals Target cell (c) Hormonal signaling
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The Three Stages of Cell Signaling: A Preview
Cells receiving signals go through 3 processes: Reception Transduction Response Animation: Overview of Cell Signaling Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
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Plasma membrane 1 Reception Receptor Signaling molecule 1
Fig EXTRACELLULAR FLUID CYTOPLASM Plasma membrane 1 1 Reception Receptor Figure 11.6 Overview of cell signaling Signaling molecule
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Plasma membrane 1 Reception Transduction Receptor Signaling molecule 1
Fig EXTRACELLULAR FLUID CYTOPLASM Plasma membrane 1 1 Reception 2 Transduction Receptor Relay molecules in a signal transduction pathway Figure 11.6 Overview of cell signaling Signaling molecule
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Plasma membrane 1 Reception Transduction Response Receptor Activation
Fig EXTRACELLULAR FLUID CYTOPLASM Plasma membrane 1 Reception 2 Transduction 3 Response Receptor Activation of cellular response Relay molecules in a signal transduction pathway Figure 11.6 Overview of cell signaling Signaling molecule
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A signaling molecule is called a ligand
Concept 11.2: Reception: A signal molecule binds to a receptor protein, causing it to change shape A signaling molecule is called a ligand Most signal receptors are plasma membrane proteins Binding between a ligand & receptor is highly specific A receptor shape change is often the initial transduction of the signal Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
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Receptors in the Plasma Membrane
There are three main membrane receptor types: G protein-coupled receptors Receptor tyrosine kinases Ion channel receptors Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
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G protein-coupled receptor:
A plasma membrane receptor Works with the help of a G protein The G protein: Acts as an on/off switch Inactivated by binding to GDP Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
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Signaling-molecule binding site
Fig. 11-7a Signaling-molecule binding site Figure 11.7 Membrane receptors—G protein-coupled receptors, part 1 Segment that interacts with G proteins G protein-coupled receptor
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Figure 11.7 Membrane receptors—G protein-coupled receptors, part 2
Fig. 11-7b Plasma membrane G protein-coupled receptor Inactive enzyme Activated receptor Signaling molecule GDP G protein (inactive) Enzyme GDP GTP CYTOPLASM 1 2 Activated enzyme Figure 11.7 Membrane receptors—G protein-coupled receptors, part 2 GTP GDP P i Cellular response 3 4
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Receptor tyrosine kinases:
Are membrane receptors Attach phosphates to tyrosines A receptor tyrosine kinase can trigger multiple signal transduction pathways at once Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
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Fully activated receptor tyrosine kinase
Fig. 11-7c Signaling molecule (ligand) Ligand-binding site Signaling molecule Helix Tyr Tyr Tyrosines Tyr Tyr Tyr Tyr Tyr Tyr Tyr Tyr Tyr Tyr Tyr Tyr Tyr Tyr Tyr Tyr Receptor tyrosine kinase proteins Dimer CYTOPLASM 1 2 Activated relay proteins Figure 11.7 Membrane receptors—receptor tyrosine kinases Cellular response 1 Tyr Tyr P Tyr Tyr P Tyr Tyr P P Tyr Tyr P Tyr Tyr P Tyr Tyr P P Cellular response 2 Tyr Tyr P Tyr Tyr P Tyr P Tyr P 6 ATP 6 ADP Activated tyrosine kinase regions Fully activated receptor tyrosine kinase Inactive relay proteins 3 4
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A ligand-gated ion channel receptor:
A ligand-gated receptor Acts as a gate for ion movement Signal molecule (ligand) binding results in: Change in receptor shape Creation of a channel in the receptor Transport of specific ions, e.g. Na+ or Ca2+ Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
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1 Signaling molecule (ligand) Gate closed Ions Plasma membrane
Fig. 11-7d 1 Signaling molecule (ligand) Gate closed Ions Plasma membrane Ligand-gated ion channel receptor 2 Gate open Cellular response Figure 11.7 Membrane receptors—ion channel receptors 3 Gate closed
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Intracellular Receptors
Found in the cytosol or nucleus of target cells Small or hydrophobic chemical messengers: Can readily cross the membrane Can activate receptors Examples of hydrophobic messengers: Steroid & thyroid hormones of animals An activated hormone-receptor complex: Can act as a transcription factor Turning on specific genes Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
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Hormone (testosterone) Plasma membrane Receptor protein DNA NUCLEUS
Fig Hormone (testosterone) EXTRACELLULAR FLUID Plasma membrane Receptor protein DNA Figure 11.8 Steroid hormone interacting with an intracellular receptor NUCLEUS CYTOPLASM
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Hormone (testosterone) Plasma membrane Receptor protein Hormone-
Fig Hormone (testosterone) EXTRACELLULAR FLUID Plasma membrane Receptor protein Hormone- receptor complex DNA Figure 11.8 Steroid hormone interacting with an intracellular receptor NUCLEUS CYTOPLASM
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Hormone (testosterone) Plasma membrane Receptor protein Hormone-
Fig Hormone (testosterone) EXTRACELLULAR FLUID Plasma membrane Receptor protein Hormone- receptor complex DNA Figure 11.8 Steroid hormone interacting with an intracellular receptor NUCLEUS CYTOPLASM
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Hormone (testosterone) Plasma membrane Receptor protein Hormone-
Fig Hormone (testosterone) EXTRACELLULAR FLUID Plasma membrane Receptor protein Hormone- receptor complex DNA Figure 11.8 Steroid hormone interacting with an intracellular receptor mRNA NUCLEUS CYTOPLASM
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Hormone (testosterone) Plasma membrane Receptor protein Hormone-
Fig Hormone (testosterone) EXTRACELLULAR FLUID Plasma membrane Receptor protein Hormone- receptor complex DNA Figure 11.8 Steroid hormone interacting with an intracellular receptor mRNA NUCLEUS New protein CYTOPLASM
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Signal transduction usually involves: Multistep pathways:
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 amplify a signal A few molecules can produce a large cellular response Multistep pathways provide: More opportunities for coordination & regulation of the cellular response Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
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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 shape change in a protein Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
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Protein Phosphorylation and Dephosphorylation
In many pathways, signals are transmitted by cascades of protein phosphorylations Protein kinases: Transfer phosphates from ATP to protein The process called phosphorylation Protein phosphatases: Remove the phosphates from proteins The process called dephosphorylation The phosphorylation-dephosphorylation system: Acts as a molecular switch Turns activities on and off Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
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Phosphorylation cascade
Fig. 11-9 Signaling molecule Receptor Activated relay molecule Inactive protein kinase 1 Active protein kinase 1 Inactive protein kinase 2 ATP Phosphorylation cascade ADP Active protein kinase 2 P PP P i Figure 11.9 A phosphorylation cascade Inactive protein kinase 3 ATP ADP Active protein kinase 3 P PP P i Inactive protein ATP ADP P Active protein Cellular response PP P i
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End of The Chapter
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