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Chapter 11
Communication
Cell communication
Traditional Ethiopian coffee ceremony
Caffeine
Sends signals to Blood vessels Brain Liver Heart
Yeast cells
Bacteria
NO
Cell communication
Coordinates cell behavior Body functions as a whole. Hallmark of multicellular organisms. Evolution Single cell organisms communicate.
Cell communication
Cells are exposed to a continuous stream of signals.
Signals come from the environment surrounding the cell.
Signals can be from another cell. Chemical signals
Chemical signals
Peptides Proteins Amino acid Nucleotides Steroids or other lipids NO or Nitric oxide
Types of cell signaling
Depend on location of cells 1. Direct contact 2. Local signaling A. Paracrine signaling B.Synaptic signaling 3. Long-distance signaling Endocrine Nerve electrical impulse
1. Direct contact
Gap junction: Animal cells Plasmodesmata: Plant cells Chemical or electrical impulse
1. Direct contact
When cells are closeMolecules on one cell are
recognized by the plasma membrane of another cell.
Many interactions between cells in early development occur this way.
2. Local signaling
A. Paracrine signalingShort-lived signals with local
effects.Growth factorsPlay an important role in early
development
Local signaling
B. Synaptic signaling Involves the nervous systemNeurotransmitters: Signal moleculesChemical synapse: Communication be neuron & the
target cell
Long distance Signaling
Endocrine signalingMolecules that remain in the
extracellular fluid Enter the bloodstreamAffect cells very far from where
releasedHormones: longer-lived signal molecules
Long distance signaling
Nerve cellElectrical impulse along the
neuron
Signal transduction pathway
The signal causes a response in the cell
Fig. 11-14
Growth factor
Receptor
Phosphorylationcascade
Reception
Transduction
Activetranscriptionfactor
ResponseP
Inactivetranscriptionfactor
CYTOPLASM
DNA
NUCLEUS mRNA
Gene
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Signal transduction pathway
Reception:Signal is detectedMolecule binds a receptor
protein Located on surface or inside
Signal transduction pathway
Transduction:Signaling molecule changes
receptorChanges signal so it can cause a
responseSingle stepMultiple steps
Signal transduction pathway
Response:Stimulates a specific cellular
responseCorrect cellCorrect response
Reception
Ligand:Molecule that binds specifically to
another moleculeActivates the receptor proteinReceptor protein undergoes change
in shape
Reception
Most receptors are plasma membrane proteins
Signal (ligand) large, water soluble
Receptors
A. Intracellular receptors.B. Cell surface receptors.1. Ion-channel receptors2. Tyrosine kinases3. G-protein-coupled receptors
A. Intracellular receptors
Lipid-soluble signaling molecule Small molecule Able to cross the membrane Interacts with a receptor inside. Bind protein receptors in the cytoplasm Bind protein receptors in the nucleus
A. Intracellular receptors
1. Act as regulators of gene expression
Activate or suppress expression of certain genes
Cortisol, testosterone, estrogen & progesterone are signal molecules.
Fig. 11-8-5 Hormone(testosterone)
EXTRACELLULARFLUID
Receptorprotein
Plasmamembrane
Hormone-receptorcomplex
DNA
mRNA
NUCLEUS New protein
CYTOPLASM
A. Intracellular receptors
2. Receptors act as enzymes Example: NO Binds a receptor. Activates the enzyme to catalyze the
synthesis of GMP Relax smooth muscle Causing blood vessels to relax Causes an increased blood flow
B. Cell surface receptors
Many signal molecules are water soluble Unable to pass through membrane Bind a receptor on the surface Causes a change inside cell.
B. Cell surface receptors
1. Ion channels (Chemically gated) Receptor proteins that allow ions to pass
through Opens only when a signal molecule (ligand)
binds to receptor. Ions are sodium, potassium, calcium or chlorine. Gate closes when ligand is released Example of signal molecule-neurotransmitter
2. Tyrosine Kinases
Single molecules bind receptor outside the cell
Stimulates receptor to activate the enzyme in the cytoplasm
These enzymes catalyze the transfer of phosphate groups
2. Tyrosine Kinases
Phosphorolated receptor Addition of phosphates to
receptorTriggers a cell responseCan trigger more than one
response
Fig. 11-7c
Signalingmolecule (ligand)
Ligand-binding site
Helix
TyrosinesTyr
Tyr
Tyr
Tyr
Tyr
Tyr
Receptor tyrosinekinase proteins
CYTOPLASM
Signalingmolecule
Tyr
Tyr
Tyr
Tyr
Tyr
Tyr
Tyr
Tyr
Tyr
Tyr
Tyr
Tyr
Dimer
Activated relayproteins
Tyr
Tyr
Tyr
Tyr
Tyr
Tyr
P
P
P
P
P
P
Cellularresponse 1
Cellularresponse 2
Inactiverelay proteins
Activated tyrosinekinase regions
Fully activated receptortyrosine kinase
6 6 ADPATP
Tyr
Tyr
Tyr
Tyr
Tyr
Tyr
Tyr
Tyr
Tyr
Tyr
Tyr
Tyr
P
P
P
P
P
P
1 2
3 4
G-protein coupled receptor
G-protein coupled receptor
G-protein
GDP vs GTP
3. G-protein-linked receptors
G-protein Inactive: GDP (guanosine diphosphate) Active: GTP (guanosine triphosphate) Signal molecule binds the receptor Activates the receptor Activates the G-protein G-protein then initiates a series of events It can open an ion channel or stimulate an
enzyme
G-protein
It is a short lived response Dependent on continued extracellular
stimulation
Fig. 11-7b
G protein-coupledreceptor
Plasmamembrane
EnzymeG protein(inactive)
GDP
CYTOPLASM
Activatedenzyme
GTP
Cellular response
GDP
P i
Activatedreceptor
GDP GTP
Signaling moleculeInactiveenzyme
1 2
3 4
Transduction
Relay of signals from receptors to target cell
Multiple stepsAmplify the signalCoordination of simple
processes
Transduction
Proteins (signal molecule)Phosphorylation cascadeTransfer a phosphate from an ATP to a
protein Enzyme: protein kinaseProtein causes cellular responseAbnormal kinase activity can result in
abnormal cell growth or cancer
Phosphorylation cascade
Inactivation
Protein phosphatasesEnzymes that remove phosphatesTurns off mechanismBalance of the
phosphorylation/dephosphorylation regulate activities of the cell
Second messengers
Non-protein, small, water-soluble molecules or ions
Diffuse quickly in the cytoplasmRelay messages from the receptor
to the target cellsG protein-coupled & tyrosine kinase
pathways
Second messengers
Cyclic AMP (cAMP) Cyclic adenosine monophophateCalcium ions
cAMP pathway
Signal molecule attaches to the surface receptor.
Activates the G receptor Activates the enzyme adenylyl cyclase to
make cAMP. cAMP then activates the target protein
cAMP pathway
Amplifies signalShort-livedPhosphodiesterases (enzyme)Converts cAMP to AMP
cAMP pathway
cAMP pathway
cAMP pathway
Cholera
BacteriaCauses diarrheaToxinBlocks the inhibitory enzymeG-protein remains active-Stimulates adenylyl cyclaseMakes excessive amounts of cAMPCauses intestines to secrete ions (salts)
Nitrates
Smooth muscle relaxationDilation of blood vesselsBlock the inhibitory enzyme Prolongs cGMPContinues affect
Calcium ions
Ca ion cytoplasmic levels usually low
Increased Ca levels can causeMuscle contractionCell divisionHormone release
Calcium ions
Signal molecule attaches to the surface receptor
Activates the G receptor Which activates the enzyme phospholipase
C. Which activates IP3
Which causes the ER to release Ca ions Ca ions cause affect
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Response
Regulation of a cellular activityNucleus or cytoplasmProtein synthesisActivity of a protein
Response
Fine-tuningAmplificationSpecificityScaffolding proteinHelps enhance response
Apoptosis
Programmed cell deathChop cells that are damagedProtects surrounding cellsEmbryonic cell growth
Fig. 11-19
2 µm
Apoptosis
Caspase Enzymes that regulate cell deathSignal outside of cellNucleus can signal (DNA gone bad)ER (Protein misfolding)
Apoptosis
Webbed feet or handsParkinson’s or Alzheimer’sCancer (melanoma)
Fig. 11-21
Interdigital tissue 1 mm
