Module 3 Week One
Module 3 Week One BIOL 1520 L
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This 4 page Class Notes was uploaded by Natalie Seman on Monday October 5, 2015. The Class Notes belongs to BIOL 1520 L at Georgia Institute of Technology taught by Dr. Green in Summer 2015. Since its upload, it has received 16 views. For similar materials see Intro to Organismal Biol in Biology at Georgia Institute of Technology.
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Date Created: 10/05/15
Module 3 Week of September 28 2015 Intro to Chemical Signaling and Signal Transduction Intercellular connections are the basis of multicellularity Epithelium tissue that forms internalexternal surfacesform layers to separate organs Important for cellcell binding 0 Indirect Intercellular Attachment Plants Mddle Lamina gelatinous pectin material exists between primary cell walls or adjacent plants Acts as glue between the cell walls 39 Animals Integiins connect cytoskeleton of each cell to extracellular matrix PolysacchaIideProteoglycan Glue like a middle lamina runs between animal cells Reinforced by collagen bers 0 Tight Junctions animals 39 Cellcell attachment in plasma membrane of adjacent cells 39 Form a watertight seal commonly found in barrier cells epithelium and restrict the passive movement of substances 39 Open close based on environment conditions 39 Can be easily broken 0 Desmosomes animals 39 Cellcell attachments common in animal epithelium and muscle cells 39 Integral membrane proteins form bridges between anchoring proteins reinforced by intermediate filaments that attach to cytoplasm protein 39 Continuous support system between all cells in tissue 39 Selective adhesion cells aggregate based on their origin because of cell adhesion proteinreceptor selectivity o CellCell adhesion proteins 39 Antibody protein produced by immune response 39 Can target protein structure or interfere with interaction capacity 39 If treatment with an antibody prevents cellcell attachment antibody is bound to an adhesion protein Cadherins attachment molecules in desmosomes Cell Communication CellCell Gaps Membrane Channels 0 Signals may alter protein production at gene expression level 0 Signals may activate deactivate that already exist 0 Gap Junctions Animals 39 Connect cells via protein channels rapid passage or regulatory ions molecules 0 Plants 39 Cell walls prevent direct interaction between membrane proteins 39 Plasmodesmata allow plasma membrane and cytoplasm of adjacent cells to be continuous Smooth ER extends tubular extensions to run through portal 39 Plasma Membrane separates tissues into 1 symplast continuous network of cytoplasm connected by plasmodesmata 2 apoplast region outside the plasma membrane 0 consists of cell walls middle lamella air spaces small molecules can move through plant tissue in either compartment without ever crossing membrane Distant Cell Communication hormones acto on distant target cells by secretion into body uids 0 small present in small concentrations critical quality of signaling molecule lipid solubility o hydrophobiclipid soluble able to diffuse across hydrophobic region of plasma membrane and enter cytoplasm o hydrophiliclipid insoluble do not cross plasma membrane must be recognized at cell SUIface Signal Reception 0 Receptor molecules 39 Receptorprotein speci c though all cells receive the signal but may not respond Undergo a conformation change when hormone binds 39 Coordination identical receptors in different cellstissues may have same receptor molecule 39 1 Receptors are dynamic number of receptors may decrease if hormonal stimulation occurs highly over long time interval sensitivity of a cell 39 2 Receptors can be blocked beta blockers block adrenaline o mostly located in the plasma membrane can bind to signaling molecules that cannot cross membrane lipid insoluble o or inside cell where lipidsoluble 0 Signal receptors protein that changes conformation after binding to a signaling molecule 39 Signal ProcessingTransduction o LipidSoluble Signals 39 Processed directly With no intermediate steps 0 LipidInsoluble Signals 39 Signal molecule bound to cell surface triggers signal transduction Converts extracellular signal to intracellular signal 39 Ampli cation of INTRAcellular signals EX hormones in small concentrations trigger large response 0 Signal Transduction 39 GProtein Coupled Receptors GTP binds to G protein adds negative charge that alters protein shape Type of guanine nucleotide they re bound to regulates activityGTP GD P o Activatied When bound to GTP o Inactivated When Pi leaves to form GDP 1 Receptor transmembrane protein With intracellular portion coupled to Gprotein 2 Receptor changes shape and activates G protein 0 Discharges GDP from inactive G protein and GTP binds o GTP binding subunit breaks off 39 3G protein interacts With enzyme in plasma membrane Stimulates second messenger non protein signaling molecule that elicits intracellular response to lst messenger 0 Second Messengers small diffuse rapidly produced quickly in large quantity 39 Aren t restricted to one cell type 39 More than one involved in same signaling molecule Because arrival of single molecule can stimulate the production of many second messengers this is an ampli cation of the oniginal signal 39 EnzymeLinked Receptors Directly catalyze reaction eX RTK receptor tyrosine kinase 0 1hormone binds to RTK o 2protein forms a dimer catalytic activity is activated 39 phosphorylates itself using ATP 0 3proteins bind to RTK form a bridge btvvn receptor and peripheral membrane proteins Ras a Gprotein 39 RTK bridge activates Ras Exchange GDP for GTP o 4 Ras activation triggers phosphorylation protein kinase and activation of another protein 39 EnzymeLinked Receptors cont phosphorylation cascade o MAPK mitogen activated protein kinases 39 Mitogen activate cell division mitosis o Activated enzymes at a given stage in cascade exist in greater numbers than enzymes that preceded them 39 Original signal ampli ed many times over 0 Scaffolding proteins hold proteins in phosphorylation cascade close together 39 Limits the ampli cation of response 39 Increases speed of reaction sequence Signal Deactivation o G protein coupled reactions 39 After G proteins turn on enzymes GTP is hydrolyzed to GDP and Pi G protein conformational change 39 Second messenger presence is shortlived Once absent from cytosol reaction stops 0 Phosphorylation Cascades 39 Sensitive to the presence of external signal 39 Phosphatase enzyme removes phosphate groups 0 Shut down quickly 39 Sensitive to small changes in concentration Mutations o If hydrolysis of GTP is defective Ras which is active when bound to GTP will always be in active state and stimulate a continuous phosphorylation cascade 39 Never ending mitotic cue Crosstalk o Signals from different pathways can interact to modify response 39 Inhibitionampli cation 39 Multiple steps many points for in uence Unicellular Signaling 0 Sexual Reproduction in yeast 39 a cells and alpha cells 39 pheromones are secreted by each cell type and opposites mate yeast cells are nonmotile so the pheromones direct growth in the direction of the signal uses both g protein coupled receptors and phosphorylation cascated o actin microfilaments
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