Phospholipid bilayer hydrophilic and hydrophobic portions Integral

Phospholipid bilayer hydrophilic and hydrophobic

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Phospholipid bilayer – hydrophilic and hydrophobic portions Integral proteins/transmembrane – span the bilayer Peripheral proteins – found on the outer or inner surfaces Glycoproteins – act mainly as cell identifiers. Binding of hormones can activate different types of proteins Channel proteins Act as channels for water soluble solutes Some channels are powered by ATP Membrane protein enzymes Act as an enzyme when stimulated Adenylate cyclase is one example Receptor proteins 1 st messenger is the hormone (ligand) binding to receptor triggers activation of 2 nd messengers within the cell direct phosphorylation as a result protein based attracted to hydrophilic portions of cell membrane- rapid response rate steroids, lipids, cholesterol derived, attracted to hydrophobic slide between heads of phospholipids and pass freely through lipid bilayer- slower response rate 4
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Nur 0013 cAMP messenger system (an example of a second messenger system) Ca++ calmodulin complex (another type of 2 nd messenger system) (DAG and IP3 are second messengers, work together to increase cascade effect) Neuro hormones (secreted by hypothalamus and adrenal medulla) use this pathway 5
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Nur 0013 6
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Nur 0013 E. Hormone-Target Specificity 1. Hormone Receptors Are 3D shaped protein or glycoprotein receptors on the surface of the cells of the target tissues . Each receptor is specific to its own type of hormone. e.g. - square block in square hole e.g. – thyroid hormone will not bind to insulin receptors. Hormone-receptor interaction depends on 1. blood levels of hormone 2. relative number of receptors on target cells 3. Affinity of the bond between the hormone and receptor High vs. low affinity Hormone-receptor complexes are very specific Only hormones with a corresponding shape will activate them 2. Down Regulation and Up Regulation of receptors 7
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Nur 0013 Down regulation Occurs when a target cell has been exposed to a hormone for a prolonged period of time, causes fatigue of receptors on target tissue. Makes target cell less responsive to hormone over time bc of less receptors
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