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Reading: Campbell and Reece, 2002: Chapter 11 - Cell 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).  
   
   
   
2. 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.  Cellular activities that respond to these influences include such functions as cell division, cellular metabolism, and gene expression.
   
   
   
3. Cell-cell interactions are achieved by direct cell-cell contact, or by indirect associations among cells separated by greater or lesser distances.  Direct cell-cell communication may occur through transmembrane molecular signaling or through intercellular connections - gap (communicating) intercellular junctions (animals) or plasmodesmata (plants) (See Campbell et al., Chapter 7).  Indirect interactions are mediated by soluble factors that diffuse over greater or lesser distances and interact with specific cell membrane-associated receptor molecules.  Soluble factors may act on the cell producing the factor (autocrine regulation), on other cells locally (paracrine regulation), or on cells far removed from the source (endocrine regulation).
   




4. In addition to communication, direct cell-cell interactions may be adhesive interactions through cell adhesion molecules (CAMs), cadherins, or adhering-types of intercellular junctions. 
   
   


5. 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.
   
   
   
6. 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.