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Cell-Cell Interactions

Chapter 7

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Outline

• 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

• 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 immunochemistrymolecular genetics

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Cell Signals

• Direct contact• Paracrine signaling• Endocrine signaling

– hormones• Synaptic signaling

– neurotransmitters

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Cell Signaling

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Intracellular Receptors

• 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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Intracellular Receptors

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Cell Surface Receptors

• 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

• Second messengers relay messages from receptors to target proteins.

– cAMP– calcium

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Second Messengers

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Amplifying the Signal

• 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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Signal Amplification

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Expression of Cell Identity

• Cells contain an array of marker proteins located on the cell surface.

– glycolipids - tissue-specific cell surface markers

– MHC proteins - identify self versus non-self cells

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Intercellular Adhesion

• 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

– 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

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