lecture 13 biao ding

lecture 13 biao ding - Biol 113 AU2010 Lecture 13 Cell-Cell...

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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
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