CellCell Interactions

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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
• immunochemistry
• molecular 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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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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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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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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