Cell-Cell Interactions
Chapter 7
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Outline
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Cell Signaling
Receptor Proteins
– Intracellular Receptors
– Cell Surface Receptors
Initiating the Intracellular Signal
Amplifying the Signal
Expression of Cell Identity
Intercellular Adhesion
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Cell Signaling
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Receptor proteins have a three-dimensional
shape that fits a specific signal molecule.
– When a signal molecule and receptor
protein bind, a change in the receptor
protein is induced and a response in the
cell is generated.
 investigation tools
 immunochemistry
 molecular genetics
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Cell Signals
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Direct contact
Paracrine signaling
Endocrine signaling
– hormones
Synaptic signaling
– neurotransmitters
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Cell Signaling
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Intracellular Receptors
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Intracellular receptors are located within the
cell, and trigger a variety of responses,
depending on the receptor.
– acting as gene regulators
– acting as enzymes
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Cell Surface Receptors
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Extracellular signals converted to intracellular
– chemically-gated ion channels
 open or close when signal molecules bind
to the channel
– enzyme receptors
 usually activate intracellular proteins by
phosphorylation
– G-protein receptors
 activate intermediary protein
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Cell Surface Receptors
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Initiating the Intracellular Signal
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Second messengers relay messages from
receptors to target proteins.
– cAMP
– calcium
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Amplifying the Signal
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Most signaling molecules exist in such low
concentration, diffusion across the
cytoplasm requires amplification.
– A single cell surface receptor can
stimulate a cascade of protein kinases to
amplify the signal.
 causes a strong response inside the cell
to a weak signal outside
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Signal Amplification
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Expression of Cell Identity
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Cells contain an array of marker proteins
located on the cell surface.
– glycolipids - tissue-specific cell surface
markers
– MHC proteins - identify self versus nonself cells
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Intercellular Adhesion
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Cell junctions are long-lasting or permanent
connections with each other.
– tight junctions - connect plasma
membranes of adjacent cells in a sheet,
preventing small molecules from leaking
between the cells
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Intercellular Adhesion
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anchoring junctions - mechanically attach
the cytoskeleton of a cell to the
cytoskeletons of other cells or the
extracellular matrix
communicating junctions - chemical or
electrical signal passes directly from one
cell to an adjacent cell
 gap junctions - animals
 plasmodesmata - plants
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Cell Junctions
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Summary
•
•
•
•
•
•
Cell Signaling
Receptor Proteins
– Intracellular Receptors
– Cell Surface Receptors
Initiating the Intracellular Signal
Amplifying the Signal
Expression of Cell Identity
Intercellular Adhesion
19
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