3)Four features of signal-transducing systems Part II Structure and Catalysis (a)Specificity (c) Desensitization/Adaptation Signal molecule fits Receptor activation triggers binding site on its a feedback circuit that shuts off the receptor or removes Receptor complementary receptor other signals do not fit. Receptor it from the cell surface Effect Response (b)Amplification (d)Integration when enzymes activate Signal When two signals have Signal 1 Signal 2 enzymes, the number of opposite effects on a affected molecules metabolic characteristic increases geometrically such as the concentration in an enzyme cascade. Enzyme 1 of a second messenger X, Receptor(Receptor or the membrane potential results from the integrated input from both receptors.↑ X]or TV↓ X]or v Net△ X]or v name 3313 Response
(3) Four features of signal-transducing systems
(4)Different cells can respond differently to the same extracellular signal molecule IC)skeletal muscle cell A heart muscle cell (B》 salivary gland cell receptor … secreTION acetylcholine DECREASED RATE AND CONTR FORCE OF CONTRACTION Various responses induced by neurotransmitter acetylcholine
(4) Different cells can respond differently to the same extracellular signal molecule Various responses induced by neurotramsmitter acetylcholine
(5)A cell can remember the effect of some signals, after the signal has disappeared.(Ca2+) Protein kinase activited by Cat to phosphorylate itself and other proteins, the autophosphorylation keeps the kinase active long after Cat levels return to normal Transient extracellular signals often induce much longer-term changes in cells during the development of a multicellular organism. They usually depend on self- activating memory mechanisms that operate further downstream in a signaling pathway, at the level of gene transcription
(5) A cell can remember the effect of some signals, after the signal has disappeared. (Ca2+) Protein kinase activited by Ca2+ to phosphorylate itself and other proteins, the autophosphorylation keeps the kinase active long after Ca2+ levels return to normal. Transient extracellular signals often induce much longer-term changes in cells during the development of a multicellular organism.They usually depend on selfactivating memory mechanisms that operate further downstream in a signaling pathway,at the level of gene transcription
B. Signal Molecules and Receptors (1)Signal molecules Some Signals to Which Cells Respond Antigens Cell surface glycoproteins/oligosaccharides Developmental signals Extracellular matrix components Growth factors Hormones Light Mechanical touch Neurotransmitters Odorants Pheromones Tastants
B. Signal Molecules and Receptors (1) Signal molecules:
(2) Receptors include two classes: A ION-CHANNEL-LINKED RECEPTOR CELL- SURFACE RECEPTORS plasma plasma membran cell-surface receptor 1B) G-PROTEIN-LINKED RECEPTOR hydrophilic signa molecule INTRACELLULAR RECEPTORS small hydrophobic ignal molecule activated zyme G protein IC) ENZYME-LINKED RECEPTORS carrier protein gnal molecule in form of a dimer nucleus intracellular receptor inactive catalytic active catalytic domain
(2) Receptors include two classes: