Refers to intercellular mechanisms that mediate

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Refers to intercellular mechanisms that mediate response of target cell to chemical messenger o Downstream of receptor-ligand binding o Lipophilic messengers: receptors typically intracellular Philic = loving o Lipophobic messengers: receptors on membrane surface Phobic = hating - Second messenger o First messenger is the ligand that binds to the receptor o Second messenger: an intracellular messenger produced by the binding of an extracellular messenger Will bind to the outside of the membrane o The only time a second messenger is needed is when the first ligand can’t bind to the receptor o Lipophilic signaling First messenger that crosses the membrane Can bind to a messenger either outside or inside the nucleus of the membrane End up binding to a HRE A hormone response element: change in gene expression; will either make more protein or less protein o If they are not lipophilic, they are Lipophobic and go through a membrane receptor- mediated signal transduction pathways Fast channel-linked Calcium, sodium, chloride, potassium, etc. Receptors > messenger binds to a receptor, opens up to the channel and allows ions to go through Enzyme linked Receptors > messenger binds to receptor that is inactive; when binds to the receptor, it becomes active (tyrosine kinase = phosphorylate something) This pathway can result in a lot of different things. Has had a lot of attention in certain types of cancer o Dimerization Have two tyrosine kinases in the membrane; whenever the messenger binds to both of them it causes a process called dimerization. When dimerization occurs, its like turning on the on switch, meaning whatever was coupled gets the binding of the receptor o Initiates cell division Cervical cancer has become more and more common. Cause by HPV. What HVP does that it is so tough to combat, HPV produces a protein called E5. E5 binds to receptors in cell in a women’s cervix and can cause dimerization. Dimerization will let the cell do whatever it is programed to do (may be cell division)
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23 G-proteins Slow channel-linked cAMP cGMP Phosphatidylinositol G-proteins are small intracellular proteins that link receptors with effector proteins o Called molecular ?? o Bond to GTP = active o Bod to GDP = inactive o GTPase = breaks down GTP If it breaks GTP down too slowly can result in tumor formation Receptors linked to G-proteins are called G-protein Coupled Receptors (GPCRs) Have three subunits: alpha, beta, and gamma Three types o Ion channel regulating When the messenger binds to the receptor, the GTP can bind to the messenger and can cause the function of the cell Very common pathway Differences from fast ligand gated ion channel receptors Can open AND close ion channels Open and close more SLOWLY Stay open LONGER o Enzyme inhibiting (G i )/regulating Produce second messengers in cytosol 5 major second messenger pathways regulated by G- proteins cAMP cGMP IP3 DAG
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