Signal Transduction & Changes in Pathways PDF
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This document explores signal transduction pathways in cells. It describes how cells communicate and the different types of membrane receptors involved in this process, including ligand-gated ion channels, catalytic receptors, and G-protein-linked receptors. The document also explains feedback mechanisms, including negative and positive feedback.
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Signal Transduction & Changes In Pathways T he cells of multi-celled organisms must communicate with one another to coordinate the activities of the organism as a whole. Cells communicate through cell-to-cell contact or through cell signaling. Signaling can be...
Signal Transduction & Changes In Pathways T he cells of multi-celled organisms must communicate with one another to coordinate the activities of the organism as a whole. Cells communicate through cell-to-cell contact or through cell signaling. Signaling can be short-range(affecting only nearby cells) or long-range(affecting cells throughout the organism). It can be done by cell junctions or signalling molecules called ligands that bind to receptors and trigger a response by changing the shape of the receptor protein. Signal transductionis the process by which an externalsignal is transmitted to the inside of a cell. It usually involves the following three steps: 1. a signaling molecule binding to a specific receptor 2. activation of a signal transduction pathway 3. production of a cellular response For signaling molecules that cannot enter the cell, a plasmamembrane receptor is required. Plasma membrane receptors form an important class of integral membrane proteins that transmit signals from theextracellular space intothe cytoplasm. Each receptor binds a particular molecule in a highly specific way. There are three classes of membrane receptors. 1. L igand-gated ion channelsin the plasma membrane openor close an ion channel upon binding a particular ligand. This channel opens in response to acetylcholine, and a massive influx of sodium depolarises the muscle cell and causes it to contract. 2. Catalytic (enzyme-linked) receptorshave an enzymaticactive site on the cytoplasmic side of the membrane. Enzyme activity is initiated by ligand binding at the extracellular surface. 3. AG-protein-linked receptordoes not act as an enzyme,but instead will bind a different version of a G-protein (often GTP or GDP) on the intracellular side when a ligand is bound extracellularly. This causes activation of secondary messengers within the cell. One important second messenger is cyclic AMP (cAMP). Signal transduction cascadesare helpful to amplifya signal. FEEDBACK T he set of conditions under which living things can successfully survive is called homeostasis. Your blood glucose levels are regulated byinsulinand glucagon, two hormones released from yourpancreas. Many of these responses are controlled bynegativeor positivefeedback pathways. A negative feedback pathway (also calledfeedbackinhibition)works by turning itself off using the end product of the pathway. The end product inhibits the process from beginning, thus shutting down the pathway. positive feedback pathway also involves an end product playing a role, but instead of A inhibiting the pathway, it further stimulates it.
