Biology 107 Cellular Communication

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Biology 107Cellular Communication

• October 7, 2002

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Cellular Communication

• Student Objectives As a result of this lecture
  and the assigned reading, you should understand
  the following
• 1. A cell communicates and interacts with other
  cells (cell-cell interactions) and with its
  extracellular matrix (ECM) (cell-matrix
  interactions)
• Extracellular communication factors are of two
  general types 1) those that get through the
  lipid bilayer on their own (e.g., steroid
  hormones) or 2) those that act on the outside of
  the membrane (e.g., peptide hormones) and require
  a receptor and transduction of the signal across
  the membrane to produce an intracellular
  response.
• Extracellular communication factors influence
  such cellular functions as cell division,
  metabolism, and gene expression.

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Cellular Communication

• 4. Cell-cell interactions are achieved by direct
  cell-cell contact, or by indirect associations
  among cells separated by greater or lesser
  distances. In addition to communication, direct
  cell-cell interactions may be adhesive
  interactions through cell adhesion molecules
  (CAMs), cadherins, or adhering-types of
  intercellular junctions.
• a. Direct cell-cell communication may occur
  through transmembrane molecular signaling or
  through intercellular connections - gap
  (communicating) intercellular junctions
  (animals) or plasmodesmata (plants).
• b. Indirect interactions are mediated by soluble
  factors that diffuse over greater or lesser
  distances and interact with specific cell
  membrane-associated receptor molecules.

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Cellular Communication

• Signal transduction may lead to receptor changes
  that directly affect intracellular events (e.g.,
  altered permeability of an ion channel) or may
  indirectly affect intracellular events through
  second messenger systems (e.g., cyclic AMP and
  diacylglycerol/inositol triphosphate messengers).
  
• Second messengers are small molecules that
  diffuse rapidly and amplify the cellular response
  by acting to directly or indirectly activate
  protein kinases, enzymes that attach phosphate
  groups from ATP to specific target proteins.
• 7. Protein phosphorylation/dephosphorylation is a
  common mode of rapid, reversible regulation of
  protein function. The protein kinases transfer
  phosphate groups to proteins, while specific
  protein phosphatases remove phosphate groups.

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Cells May Interact and Attach to Their
Non-cellular Extracellular Matrix (ECM)
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Cells May Interact Directly with Other Cells
Through Intercellular Junctions or Through Cell
Surface Molecules
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Cadherins are Examples of Adhesive Cell Surface
Molecules that Link Adjacent Cells Together
Attachment

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Direct Cell-cell Interactions May Involve
Distinct Junctions
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Some Intercellular Junctions Have Attachment as
Their Primary Function
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Tight Junctions Connect Adjacent Cells to Inhibit
Movement of Material Between Cells
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Some Intercellular Junctions Have Direct
Cell-Cell Communication as Their Primary Function
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Plasmodesmata are Direct Cytoplasmic Connections
Between Adjacent Plant Cells
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Gap Junctions are Membrane Channels That Allow
Direct Communication Between Animal Cells
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Cell May Interact Indirectly with Other Cells
Through Secreted Signal That Diffuse to the Target
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Three Major Components of Signaling are
Reception, Transduction, and the Response
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Signals Received on the Outside of the Cell May
Influence Intracellular Events such as Gene
Transcription
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Receptors Provide Specificity to Signaling
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Receptor Type Determines the Intracellular
Response to Ligand Binding
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One Consequence of Signal Transduction is
Amplification of the Response
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Second Messenger Systems Amplify the Initial
Signal and Usually Work Through a Protein Kinase
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A Common Second Messenger is cAMP
cAMP is a nucleotide cAMP activates a protein
kinase
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DAG and IP3 are Common Second Messengers
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Both cAMP and DAG/IP3 Pathways Work Through
G-Protein Intermediates
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Interactions of Different Transduction Pathways
Lead to Diversity of Responses