Week 10 Notes
Week 10 Notes BSC 450
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This 4 page Class Notes was uploaded by Jordana Baraad on Friday October 30, 2015. The Class Notes belongs to BSC 450 at University of Alabama - Tuscaloosa taught by Dr. Ramonell in Summer 2015. Since its upload, it has received 46 views. For similar materials see Fundamentals of Biochemistry in Biological Sciences at University of Alabama - Tuscaloosa.
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Date Created: 10/30/15
1028 Biological Signaling Basics of Biological Signal Transduction External signals transduced l cell response 1 Respond to environment Survival signals if can t respond need to undergo apoptosis Problems 1 How does the signal enter the cell 2 How to make the needed change Membrane Proteins Integral membrane proteins Portions that interact with the extracellular matrix ECM and cytoplasm KEY to cell functioning GPlanchored proteins Glycophosphatidylinositol anchored proteins Sugar protein phosphatidylinositol anchor Signal cleaved l sugar protein released to act in cell Anchor added posttranslationally Peripheral membrane proteins lnner or outer lea et Weak force interaction with phospholipid heads and membrane Dominant force hydrophobic interactions hold in membrane Integral membrane proteins can use dhelices to span the lipid bilayer Outer loops interact with ligands signaling molecules More variety Inner loops associate with inner G proteins Sequence Bacteriorhodpsin Primary amino acid sequence Yellow hydrophobic regions membranespanning Pink hydrophilic areas face ECM or cytoplasm interact with signaling molecules Hyrdopathy plot 7 peaks 7 hydrophobic regions 7 membranespanning regions Inference protein depicted is an integral membrane protein Integral membrane proteins can use dhelices to span the lipid bilayer Porins l bacteria mitochondria plasma membrane Only in outer membrane MUCH less speci c of 2 membranes Porin nonspeci c transporter 2 types receptors membrane 1 Housekeeping proteins present in all cells 2 Speci c proteins only present in particular cells tissue types Signal transduction pathwavs convert the presence of biolooical molecules into physical responses Signal not received if receptors not present to quothearquot it Signal binding change in receptor s shape l movement l changed interaction between receptor and cell l signaling cascade 3 receptor binds signal Left G protein coupled Signal cascade signal transduction pathway Right receptor tyrosine kinase Tyrosine predominant type kinase in animals More minor seronine threonine kinases Predominate in plants Purple bottom nal product Crosstalk communication between signaling pathways l more info about stressor pathogen Multiple pathways multiple products possible Six general types of signal transducers in the cell 2 2 subunits come together l phosphorylation 3 Form cGMP 4 speci c response to extracellular ligand simplest type of binding I cell channel opening 5 integrins interact with ECM short tails to clamp onto cytosketon on cytoplasmic side physical transduction across membrane bent off straight on recruits adapters Gprotein coupled receptors GPCR s Beststudied receptors targeted by 50 of drugs Ex Beta blocker suppresses ght ight impulse to calm nerves 3 outer loops bind epinephrine 3 inner loops associate with Gprotein GDPbound off GTPbound on Dissociation l active effector typically an enzyme Beta unit no lipid tail Factors involved in the sensitivity of signaling molecules 1 a Speci city 2 b Ampli cation signal made stronger a fast can happen in 1 ms 3 d desensitization feedback inhibition turn offdown signal 4 e integration crosstalk between pathways a antagonistic result addition of 2 pathways i can tell which predominates 5 c signaling module complex a key to building phosphorylation i forms new binding site Pathway to the synthesis of the second messenger by GPCR s Epinephrine bound l exchange cAMP production changes cAMP powerful second messenger Gs stimulator The Badrenergic receptor is a 7transmembrane helix protein Epinephrine bound in pocket A Gprotein is a heterotrimer made up of Ga GB and Gv GDP bound in pocket on alpha subunit Adenvlate Cvclase catalvzes the formation of cAMP Uses ATP Top right adenylate cyclase Active site bent 2 sites where chemistry takes place facing each other Binding epinephrine activates the qu protein which then activates adenylyl cyclase alpha subunit intimately associated with receptor shape change of receptor shape change in alpha change in affinity for GDP l affinity for GTP Structural Changes to BzAR upon ligand binding occur in TMS and TM6 Green TM5 shifts down compared to blue at least 2 coils TM6 swings 90 degrees ON epinephrinebound New loop formed new interactions with new Gapha subunit Movement of the TM helices creates new interactions with qu Right new loop can interact with helix FA3a phenylalanine Critical in message movement Without it binding can still occur BUT no signaling Gapha not activated Movement of the TM helices creates new interactions with qu cont Yellow Gapha Green receptor TM5 shifts down new hydrophobic pocket created so Gapha can shift up new favorable interactions qu binding to the receptor causes large conformational changes Gapha off Right green helix receptor Gray Gapha active Purple binding site ATP Yellow high affinity for GDP receptor Binding shape change affinity change in binding site binds GTP l quotonquot Termination of the signal involves multiple mechanisms 1 breakdown cAMP secondary messenger Gapha can hydrolyze GP l turns self off GSCX is a GTPase Once quotoffquot reassociates with beta and gamma subunits lnternalize receptor desensitization step JUN
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