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Unformatted text preview: 1 Biol 113 AU2010 Lecture 13 Cell-Cell Communications (II) F. Transduction: Cascades of molecular interactions relay signals from receptors to target molecules in the cell G. Response: Cell signaling leads to regulation of transcription or cytoplasmic activitiesCellular membranes are fluid mosaics of lipids and proteins H. Fine-Tuning of the response F. Transduction: Cascades of Molecular Interactions Relay Signals from Receptors to Target Molecules in the Cell • Signal transduction usually involves multiple steps • Multistep pathways can amplify a signal: A few molecules can produce a large cellular response • Multistep pathways provide more opportunities for coordination and regulation of the cellular response • The molecules that relay a signal from receptor to response are mostly proteins • \At each step, the signal is transduced into a different form, usually a shape change in a protein 1. Protein Phosphorylation and Dephosphorylation • In many pathways, the signal is transmitted by a cascade of protein phosphorylations • Protein kinases transfer phosphates from ATP to protein, a process called phosphorylation • Protein phosphatases remove the phosphates from proteins, a process called dephosphorylation • This phosphorylation and dephosphorylation system acts as a molecular switch, turning activities on and off Fig. 11-9 2. Small Molecules and Ions as Second Messengers • The extracellular signal molecule that binds to the receptor is a pathway’s “first messenger” • Second messengers are small, nonprotein, water-soluble molecules or ions that spread throughout a cell by diffusion • Second messengers participate in pathways initiated by G protein-coupled receptors and receptor tyrosine kinases • Cyclic AMP and calcium ions are common second messengers Cyclic AMP • Cyclic AMP (cAMP) is one of the most widely used second messengers • Adenylyl cyclase , an enzyme in the plasma membrane, converts ATP to cAMP in response to an extracellular signal Fig. 11-10 2...
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