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Signal transduction Parmar Krupal • General features of signal transduction • Type of cell signalling • Type of Signal transducer/Receptors signal transduction • The signal represents the information, that is detected by specific receptors and converted to a cellular response, This conversion of information into a chemical change is called signal transduction. General features of signal transduction • Four features of signal-transducing systems. • • • • Specificity Amplification Desensitization/Adaptation Integration Specificity • It is achieved by molecular complimentarity between signal and receptor and it is mediated by weak non-covalent forces. • i.e. Thyrotropin-releasing hormone triggers response in the cells of the anterior pituitary but not in hepatocyte -Which lacks receptors for this hormone. Amplification • Amplification by enzyme cascades results when an enzyme associated with a signal receptor is activated and, in turn catalyzes the activation of many molecules of a second enzyme , each of which activates many molecules of a third enzyme and so on. Desensitization/Adaptation • When a signals present continuously , desensitization of the receptor system results when the stimulus falls below a certain threshold, • the system again becomes sensitive. • Think of what happens to your visual transduction system when you walk from bright sunlight into a darkened room or from darkness into the light. ? Integration • The ability of the system to receive multiple signals and produce a unified response appropriate to the needs of the cell or organism. Different signaling pathways converse with each other at several levels, generating a wealth of interactions Type of receptors • • • • • • G protein-coupled receptors Receptor tyrosine kinases Receptor guanylyl cyclases Gated ion channels Adhesion receptors Nuclear receptors G protein-coupled receptors • G protein-coupled receptors that indirectly activate (through GTP-binding proteins or G proteins) enzymes that generate intracellular second messengers. This type of receptor is illustrated by the B-adrenergic receptors system that detects epinephrine (adrenaline). G protein-coupled receptors enzymes intracellular second messengers Receptor tyrosine kinases • Receptor tyrosine kinases, plasma membrane receptors that are also enzymes. extracellular ligand binds to receptors and receptor is activated then catalyzes the phosphorylation of several cytosolic or plasma membrane proteins. • i.e. Insulin, epidermal growth factor (EGF-R). Receptor guanylyl cyclases • Receptor guanylyl cyclases which are (plasma membrane receptors) with an enzymatic cytoplasmic domain. • The intracellular second messenger from these receptors, cyclic guanosine monophosphate (cGMP), activates a cytosolic protein kinase that phosphorylates cellular proteins and thereby Changes their activities. Gated ion channel • Gated ion channels of the plasma membrane that open and close (hence the term "gated") in response to the binding of chemical ligands or changes in transmembrane potential. • These are the simplest signal transducers. • The acetylcholine receptor ion channel is an example of this mechanism Adhesion receptors •Adhesion receptors that interact with macromolecular components of the extracellular matrix (such as collagen) and convey instructions to the cytoskeletal system about cell migration or adherence to the matrix. •Integrins illustrate this general type of transduction mechanism. Nuclear receptors • Nuclear receptors (steroid receptors) that bind Specific ligands ( such as the hormone estrogen) and alter the rate at which specific genes are Transcribed and translated into cellular proteins. Because steroid hormones function through Mechanisms intimately related to the regulation of gene expression. Thank you