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Transcript
Signal Transduction Cell Communication Membrane Proteins Cellular Communication • Cell Junctions: Interconnect adjacent cells • Anchoring junctions (desmosomes) • Abundant in tissues with high stress forces (Cardiac muscles) • Tight junctions • Forms leak-proof sheet (Epithelial cells) • Gap junctions & Plasmodesmata • Direct cytoplasmic connections • Extracellular matrix: dense mat of biomolecules • Adhesion proteins link cells to EM • Neurotransmitters: typically fast responses • Hormones: long-range, often sustained, systemic actions Initial Signals • Chemical • Electromagnetic • • • • Cations Anions Electrical gradient Magnetic force field • Pressure • Temperature • Another Cell • Extracellular Matrix • Energy Mechanisms of Cell Signaling • Signal molecule or physical factor from cell environment • Internal or External environment • Signal is “sensed” by target cell via Receptors • • • • Plasma membrane Cytoplasm Organelle Nuclear membrane /Nucleoplasm • Binding of ligand • Specificity • Agonist vs. Antagonist • Initiate Signal Transduction Pathway Variables of Signaling Systems • Distance • Neighboring cells • Organismic • Endurance of signal • Seconds to hours to years • Target cell(s) • One or many • Specificity • Full molecule or merely a hapten /molecular structure • Feedback mechanisms • Feed-forward vs. Negative feedback Calcium as 2nd Messenger Role of Cholesterol • “Good” cholesterol = high-density lipoproteins (HDL) • >56 mg/ dL blood 60%% less Alzheimer’s cases than < 38% mg/ dL blood • Cholesterol is major component of cell membranes • 25% of our total cholesterol is found in brain • Cholesterol is essential to forming connections between nerve cells • Allows creation & retention of memories • Glial cells supply neurons with cholesterol • Improves rate of nerve signal transmission • Allows neuronal connections • Lipid rafts composed of cholesterol & receptor proteins • Floating through plasma membrane prevents deactivation of protein • Statins interfere with cholesterol synthesis • May negatively affect memory in some patients
