B6A11Coordinate

Change nature of the cell longer lasting effect

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Unformatted text preview: Change nature of the cell (Longer-lasting effect) Modulation of signal effect • Priming (upregulation) Signal bindsÆ more receptors synthesized Ø more hormone can bind cell • Desensitization (downregulation) Prolonged exposure to high signal molecule levels can reduce receptor expression. * Downregulation may be avoided by pulsatile secretion of the messenger. • Receptor-mediated endocytosis Receptor-ligand complex internalized on vesicle to enhance duration of effect. Electrochemical communication Mechanisms of Messenger Action • Hydrophilic signal molecules — most amino acid class – Bind to membrane receptors on cell surface – Primary effect: turn enzymes on/off Æ D activity of cell. – Secondary effect: enzymes may produce or activate transcription factors Æ turn genes on/off. • Lipophilic signal molecules — steroids & thyroid hormones – Bind to intracellular receptors in cytoplasm or nucleoplasm – Primary effect: turn genes on/off Æ D nature of cell. – Secondary effect: gene expression may produce or...
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