<p>Cell Communication Overview</p><p> Importance of cell communication – why?  How do cells communicate? o Cell-to-cell contact – direct contact, either through surface receptors or connected cytoplasm. Ex: plasmodesmata between plant cells that allow material to be transported from cell to cell, immune system cells o Local signaling – communication over short distances by using local regulators. Ex: neurotransmitters in a synapse, quorum sensing in bacteria. o Long-distance signaling – communication over long distances using endocrine signals, or hormones. Ex: insulin, testosterone.  3 Stages of a Signal Transduction Pathway 1. Reception – . Signaling begins when a receptor (either on the plasma membrane or intracellular) recognizes a specific signal molecule (aka chemical messenger, ligand, chemical signal) [specific = one-to-one relationship]. . Recognition of signal causes a conformational change in receptor, which initiates transduction. Ex: G-protein linked receptor, receptor tyrosine kinase. . Plasma membrane receptors recognize water-soluble (polar, hydrophilic) signal molecules that cannot pass through the plasma membrane easily. . Intracellular receptors are in the cytosol or nucleus and recognize small or hydrophobic signals molecules (ex: steroids, sex hormones) that pass through the plasma membrane easily. 2. Transduction (Signaling Cascade) . Advantages of having multiple steps – amplification, opportunities for coordination/regulation . Relay proteins pass signal on usually through a conformational change (Usually phophorylation, which acts as an “on/off” switch).  Kinases – phosphorylates proteins (“on”) by transferring P from ATP to protein  Phosphatases – dephosphorylates proteins (“off”) by removing P . Second messengers also participate in transduction because they can activate relay proteins. Most common are cAMP and Ca2+. Advantageous because can diffuse quickly through cytoplasm compared to larger proteins. 3. Response . Signal transduction pathway ultimately ends in some sort of cellular response to signal. . 2 general types of responses  Nuclear Response – regulation of synthesis of enzymes and other proteins (Ex: transcription factor turns genes on/off ).  Cytoplasmic Response – regulation of enzymes that have already been synthesized (Ex: phosphorylating/dephosphorylating protein to turn on/off).  What happens when there is a change in a signal transduction pathway? o Conditions that cause a signal transduction pathway to be blocked or defective can be deleterious or prophylactic. Ex: diseases/conditions, toxins, drugs. o Know how to apply at least one example.</p>