Chapter 11 Cell Communication.

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

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 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

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 (quorum sensing) Signaling can also lead to bacteria coordinating their activities with other bacteria—such as in the creation of the fruiting bodies of “slime bacteria” 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 (diagram “a”) Animal cells may also communicate cell-cell recognition. (involving direct contact between cell-surface molecules—diagram “b”) 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 (Ex: the release of growth factors stimulate nearby cells to grow in a process called paracrine signaling. Ex: the release of neurotransmitters send messages across synapses in the nervous system in synaptic signaling) In long-distance signaling, plants and animals use chemicals called hormones Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

(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

Fig Reception —a chemical signal is “detected” when the signaling molecule binds to a receptor protein EXTRACELLULAR FLUID CYTOPLASM Plasma membrane 1 1 Reception Receptor Figure 11.6 Overview of cell signaling Signaling molecule

molecule triggers the cells response
Fig Reception —a chemical signal is “detected” when the signaling molecule binds to a receptor protein Transduction —each relay molecule brings about a change in the next molecule until the final molecule triggers the cells response 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

molecule triggers the cells response
Fig Reception —a chemical signal is “detected” when the signaling molecule binds to a receptor protein Transduction —each relay molecule brings about a change in the next molecule until the final molecule triggers the cells response 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 Response –- the specific cellular response is triggered by the last relay molecule. It can be almost any type of cellular activity

Ligand —any molecule that specifically binds to another molecule
Concept 11.2: Reception: A signal molecule binds to a receptor protein, causing it to change shape Ligand —any molecule that specifically binds to another molecule The binding between a signal molecule (ligand) and receptor is highly specific Ligand binding usually causes a shape change in a receptor which is 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 (a protein that binds GDP or GTP) The G protein acts as an on/off switch: If GDP is bound to the G protein, the G protein is inactive. If GTP binds, the G protein becomes active (see diagram) 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

Fig. 11-7b See page 211 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

A kinase is an enzyme that catalyzes the transfer of phosphate groups
Receptor tyrosine kinases are membrane receptors that attach phosphates to tyrosines A kinase is an enzyme that catalyzes the transfer of phosphate groups A receptor tyrosine kinase can trigger multiple signal transduction pathways at once Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

See page 212 Signaling molecule (ligand) Ligand-binding site Signaling
Fig. 11-7c See page 212 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 P P Tyr Tyr Tyr Tyr P Tyr Tyr P Tyr Tyr P P Tyr Tyr P Tyr Tyr P Tyr Tyr P Cellular response 2 6 ATP 6 ADP P 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

See page 213 1 Signaling molecule (ligand) Gate closed Ions Plasma
Fig. 11-7d 1 Signaling molecule (ligand) Gate closed See page 213 Ions Plasma membrane Ligand-gated ion channel receptor 2 Gate open Cellular response Figure 11.7 Membrane receptors—ion channel receptors 3 Gate closed

Intracellular Receptors
Some receptor proteins are intracellular, found in the cytosol or nucleus of target cells Small or hydrophobic chemical messengers can readily cross the membrane and activate receptors Examples of hydrophobic messengers are the steroid and 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

The steroid hormone testosterone passes through the plasma membrane
Fig Hormone (testosterone) EXTRACELLULAR FLUID The steroid hormone testosterone passes through the plasma membrane Plasma membrane Receptor protein DNA Figure 11.8 Steroid hormone interacting with an intracellular receptor NUCLEUS CYTOPLASM

Testosterone binds to a receptor protein in the cytoplasm,
Fig Hormone (testosterone) EXTRACELLULAR FLUID Plasma membrane Receptor protein Testosterone binds to a receptor protein in the cytoplasm, activating it. Hormone- receptor complex DNA Figure 11.8 Steroid hormone interacting with an intracellular receptor NUCLEUS CYTOPLASM

The hormone-receptor complex enters the nucleus and binds
Fig Hormone (testosterone) EXTRACELLULAR FLUID Plasma membrane Receptor protein Hormone- receptor complex The hormone-receptor complex enters the nucleus and binds to specific genes. DNA Figure 11.8 Steroid hormone interacting with an intracellular receptor NUCLEUS CYTOPLASM

as a transcription factor, stimulating the transcription
Fig Hormone (testosterone) EXTRACELLULAR FLUID Plasma membrane Receptor protein Hormone- receptor complex DNA Figure 11.8 Steroid hormone interacting with an intracellular receptor The bound protein acts as a transcription factor, stimulating the transcription of the gene into mRNA. mRNA NUCLEUS CYTOPLASM

into a specific protein.
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 The mRNA is translate into a specific protein. CYTOPLASM

Signal transduction usually involves multiple steps
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 and regulation of the cellular response Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

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 brought about by phosphorylation. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

Protein Phosphorylation and Dephosphorylation
In many pathways, the signal is transmitted by a cascade of protein phosphorylations Protein kinases transfer phosphates from ATP to protein, a process called phosphorylation (see diagram) Protein phosphatases remove the phosphates from proteins, a process called dephosphorylation which turns off the pathway if the initial signal is no longer present. This phosphorylation and dephosphorylation system acts as a molecular switch, turning activities on and off Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

Phosphorylation cascade
Fig. 11-9 Signaling molecule 1. A relay molecule activates protein kinase 1 Receptor Activated relay molecule 2. Active protein kinase 1 transfers a phosphate from ATP to an inactive protein kinase 2, thus activating it. Inactive protein kinase 1 Active protein kinase 1 3. Active protein kinase 2 then catalyzes the phosphorylation of protein kinase 3. Inactive protein kinase 2 ATP ADP Active protein kinase 2 Phosphorylation cascade P PP Protein phosphatases remove phosphate groups P i Figure 11.9 A phosphorylation cascade Inactive protein kinase 3 4. Active protein kinase 3 phosphorylates the final protein that brings about the cell’s response to the signal ATP ADP Active protein kinase 3 P PP P i Inactive protein ATP ADP P Active protein Cellular response PP P i

Small Molecules and Ions as Second Messengers
The extracellular signal molecule that binds to the receptor is a pathway’s “first messenger” Second messengers are small, nonprotein, water-soluble molecules or ions that spread throughout a cell by diffusion Second messengers participate in pathways initiated by G protein-coupled receptors and receptor tyrosine kinases Cyclic AMP and calcium ions are common second messengers Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

Cyclic AMP (cAMP) is one of the most widely used second messengers
Fig 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 Adenylyl cyclase Phosphodiesterase Pyrophosphate P P i ATP cAMP AMP Figure Cyclic AMP Cyclic AMP is inactivated by phosphodiesterase, an enzyme that converts it to AMP.

Many signal molecules trigger formation of cAMP (ex: epinephrine)
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 Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

First messenger Adenylyl cyclase G protein GTP G protein-coupled
Fig First messenger Adenylyl cyclase G protein G protein-coupled receptor GTP ATP Second messenger cAMP The first messenger activates a G protein- coupled receptor, which activates a specific G protein. The G protein activates adenylyl cyclase, which catalyzes the conversion of ATP to cAMP. The cAMP then acts as a second messenger and activates another protein, usually protein kinase A, leading to cellular responses. Figure cAMP as second messenger in a G-protein-signaling pathway Protein kinase A Cellular responses

Ex: Cholera, a disease that results in extremely severe diarrhea
Understanding the role of cAMP in G protein signaling pathways has allowed us to better understand how some microbes cause disease. Ex: Cholera, a disease that results in extremely severe diarrhea Cholera bacteria produce toxins that modify the G protein that regulates salt and water secretion in the intestine. The modified G protein cannot hydrolyze GTP to GDP and thus remains stuck in the active form. This continuously stimulates adenylyl cyclase to make cAMP which causes the intestinal cells to secrete large amount of salts. Water moves by osmosis into the intestines causing profuse diarrhea.

Calcium Ions and Inositol Triphosphate (IP3)
Calcium ions (Ca2+) act as a second messenger in many pathways Calcium is an important second messenger because cells can regulate its concentration Increasing the cytosolic concentration of calcium ions (which is normally low) causes many responses in animal cells, including muscle cell contraction, secretion of certain substances, and cell division. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

The calcium ion concentration in the cytosol is usually much
Fig EXTRACELLULAR FLUID Plasma membrane Ca2+ pump ATP Mitochondrion Nucleus CYTOSOL Ca2+ pump Endoplasmic reticulum (ER) Figure The maintenance of calcium ion concentrations in an animal cell Ca2+ pump ATP Key The calcium ion concentration in the cytosol is usually much lower than that in the extracellular fluid and ER. Protein pumps are used to move these ions through membranes. High [Ca2+] Low [Ca2+]

Animation: Signal Transduction Pathways
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 Animation: Signal Transduction Pathways Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

See page 218 EXTRA- CELLULAR FLUID Signaling molecule
Fig EXTRA- CELLULAR FLUID See page 218 Signaling molecule (first messenger) G protein DAG GTP G protein-coupled receptor PIP2 Phospholipase C IP3 (second messenger) IP3-gated calcium channel Figure Calcium and IP3 in signaling pathways Endoplasmic reticulum (ER) Ca2+ CYTOSOL

EXTRA- CELLULAR FLUID Signaling molecule (first messenger) G protein
Fig EXTRA- CELLULAR FLUID Signaling molecule (first messenger) G protein DAG GTP G protein-coupled receptor PIP2 Phospholipase C IP3 (second messenger) IP3-gated calcium channel Figure Calcium and IP3 in signaling pathways Endoplasmic reticulum (ER) Ca2+ Ca2+ (second messenger) CYTOSOL

EXTRA- CELLULAR FLUID Signaling molecule (first messenger) G protein
Fig EXTRA- CELLULAR FLUID Signaling molecule (first messenger) G protein DAG GTP G protein-coupled receptor PIP2 Phospholipase C IP3 (second messenger) IP3-gated calcium channel Figure Calcium and IP3 in signaling pathways Endoplasmic reticulum (ER) Various proteins activated Cellular responses Ca2+ Ca2+ (second messenger) CYTOSOL

Concept 11.4: Response: Cell signaling leads to regulation of transcription or cytoplasmic activities The cell’s response to an extracellular signal is sometimes called the “output response” 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 signaling pathways regulate the synthesis of enzymes or other proteins, usually by turning genes on or off in the nucleus The final activated molecule may function as a transcription factor Figure Nuclear responses to a signal: the activation of a specific gene by a growth factor Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

See page 219 Growth factor Reception Receptor Phosphorylation cascade
Fig Growth factor Reception Receptor Phosphorylation cascade See page 219 Transduction CYTOPLASM Inactive transcription factor Active transcription factor Figure Nuclear responses to a signal: the activation of a specific gene by a growth factor Response P DNA Gene NUCLEUS mRNA

Other pathways regulate the activity of enzymes
Fig Reception Binding of epinephrine to G protein-coupled receptor (1 molecule) Other pathways regulate the activity of enzymes See page 219 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) Figure Cytoplasmic response to a signal: the stimulation of glycogen breakdown by epinephrine Inactive phosphorylase kinase Active phosphorylase kinase (105) Inactive glycogen phosphorylase Active glycogen phosphorylase (106) Response Glycogen Glucose-1-phosphate (108 molecules)

Signaling pathways can also affect the physical characteristics of a cell, for example, cell shape. The mating of yeast cells is an example of this. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

RESULTS CONCLUSION Fig. 11-16
Wild-type (shmoos) ∆Fus3 ∆formin CONCLUSION Mating factor 1 Shmoo projection forming G protein-coupled receptor Formin P Fus3 Actin subunit Figure How do signals induce directional cell growth in yeast? GTP P GDP 2 Phosphory- lation cascade Formin Formin P 4 Microfilament Fus3 Fus3 P 5 3

Fine-Tuning of the Response
Multistep pathways have two important benefits: Amplifying the signal (and thus the response) Contributing to the specificity of the response Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

Enzyme cascades amplify the cell’s response
Signal Amplification Enzyme cascades amplify the cell’s response At each step, the number of activated products is much greater than in the preceding step Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

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

These four cells respond to the same signaling molecule
Fig Signaling molecule These four cells respond to the same signaling molecule (red) in different ways because each has a different set of proteins (purple and teal shapes). Note, however, that the same kinds of molecules can participate in more than one pathway. Receptor Relay molecules Response 1 Response 2 Response 3 Cell A. Pathway leads to a single response. Cell B. Pathway branches, leading to two responses. Figure The specificity of cell signaling Activation or inhibition Response 4 Response 5 Cell C. Cross-talk occurs between two pathways. Cell D. Different receptor leads to a different response.

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

Signaling Plasma molecule membrane Receptor Three different protein
Fig Signaling molecule Plasma membrane Receptor Three different protein kinases Figure A scaffolding protein Scaffolding protein

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

Concept 11.5: Apoptosis (programmed cell death) integrates multiple cell-signaling pathways
Apoptosis is programmed or controlled cell suicide A cell is chopped and packaged into vesicles that are digested by scavenger cells Apoptosis prevents enzymes from leaking out of a dying cell and damaging neighboring cells Apoptosis of a human white blood cell. The dying cell (right) shrinks and forms lobes (“blebs”) which will be shed as fragments and digested by scavenger Cells. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

Apoptosis in the Soil Worm Caenorhabditis elegans
Apoptosis is important in shaping an organism during embryonic development The role of apoptosis in embryonic development was first studied in the soil worm, Caenorhabditis elegans In C. elegans, apoptosis results when specific proteins that “accelerate” apoptosis override those that “put the brakes” on apoptosis Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

No death signal—as long as Ced-9 is active, apoptosis is inhibited
Fig Ced-9 protein (active) inhibits Ced-4 activity No death signal—as long as Ced-9 is active, apoptosis is inhibited Mitochondrion Ced-4 Ced-3 Receptor for death- signaling molecule Inactive proteins (a) No death signal Ced-9 (inactive) Cell forms blebs Death- signaling molecule Death signal—the binding of the death signal inactivates the Ced-9. Ced-4 and Ced-3 now direct the cascade of reactions that will lead to apoptosis of the cell. Figure Molecular basis of apoptosis in C. elegans Active Ced-4 Active Ced-3 Other proteases Nucleases Activation cascade (b) Death signal

Apoptotic Pathways and the Signals That Trigger Them
Caspases are the main proteases (enzymes that cut up proteins) that carry out apoptosis Apoptosis can be triggered by: An extracellular death-signaling ligand DNA damage in the nucleus Protein misfolding in the endoplasmic reticulum Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

Apoptosis evolved early in animal evolution and is essential for the development and maintenance of all animals Apoptosis may be involved in some diseases (for example, Parkinson’s and Alzheimer’s); interference with apoptosis may contribute to some cancers Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

Fig The embryonic development of the digits of the hands and feet is accomplished largely by the apoptosis of cells in the inter-digital spaces. Interdigital tissue 1 mm Figure Effect of apoptosis during paw development in the mouse

Reception Transduction Response Receptor Activation of cellular
Fig. 11-UN1 1 Reception 2 Transduction 3 Response Receptor Activation of cellular response Relay molecules Signaling molecule

Fig. 11-UN2

You should now be able to:
Describe the nature of a ligand-receptor interaction and state how such interactions initiate a signal-transduction system Compare and contrast G protein-coupled receptors, tyrosine kinase receptors, and ligand-gated ion channels List two advantages of a multistep pathway in the transduction stage of cell signaling Explain how an original signal molecule can produce a cellular response when it may not even enter the target cell Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

Define the term second messenger; briefly describe the role of these molecules in signaling pathways
Explain why different types of cells may respond differently to the same signal molecule Describe the role of apoptosis in normal development and degenerative disease in vertebrates Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

Chapter 11 Cell Communication.

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