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 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

Fig. 11-1 Figure 11.1 How do the effects of Viagra (multicolored) result from its inhibition of a signaling-pathway enzyme (purple)?

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

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 Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

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

Pathway similarities suggest that ancestral signaling molecules evolved in prokaryotes and were modified later in eukaryotes The concentration of signaling molecules allows bacteria to detect population density Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

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

Local and Long-Distance Signaling Cells 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 Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

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

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 Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

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

(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

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

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 Animation: Overview of Cell Signaling Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

Plasma membrane 1 Reception Receptor Signaling molecule 1 Fig. 11-6-1 EXTRACELLULAR FLUID CYTOPLASM Plasma membrane 1 1 Reception Receptor Figure 11.6 Overview of cell signaling Signaling molecule

Plasma membrane 1 Reception Transduction Receptor Signaling molecule 1 Fig. 11-6-2 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

Plasma membrane 1 Reception Transduction Response Receptor Activation Fig. 11-6-3 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

Most signal receptors are plasma membrane proteins Concept 11.2: 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 shape change in a receptor is often the initial transduction of the signal Most signal receptors are plasma membrane proteins Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

Receptors in the Plasma Membrane Most water-soluble signal molecules bind to specific sites on receptor proteins in the plasma membrane There are three main types of membrane receptors: G protein-coupled receptors Receptor tyrosine kinases Ion channel receptors Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

A G protein-coupled receptor is a plasma membrane receptor that works with the help of a G protein The G protein acts as an on/off switch: If GDP is bound to the G protein, the G protein is inactive Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

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

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

Receptor tyrosine kinases are membrane receptors that 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

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

A ligand-gated ion channel receptor acts as a gate when the receptor changes shape When a signal molecule binds as a ligand to the receptor, the gate allows specific ions, such as Na+ or Ca2+, through a channel in the receptor Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

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