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cell signaling 16
| Question | Answer |
|---|---|
| cell communication | Mechanisms by which free-living cells of a species or the cells of a multicelled organism coordinate their activities; involves sending and receiving, transducing, and responding to signaling molecules. |
| signal transduction | -message converted among different forms -signaling cell--> singnal molecule-->target cell with receptor for molecule. (receotor=protein) -extracellular signal molecule converted intracellular signal (biochmeicla or electrical) |
| widespread signal | may be neccessary in multicellular organisms, cell=endocrine ex radio/tv broadcast |
| locally acting signals | paracrine, also hormone, don't enter bloodstream, target cells lie near signalling cell, signalling cell=paracrine example posting flyers |
| specific, long-distance signals through through "private lines" | -Neuronal -signaling cells=neurons -axons up to 1m -electrical impulse signals through cell -chemical signal to target cell= neurotransmitter released to synapse |
| Shortest range signal | -direct contact with another cell -signalling molecules, receptors embeded in cell membranes -contact-dependent -important during development |
| Cells respond selectively to signals | -Depends on presence of receptor(s) -ultimate biochemical target cell and its response depend on signal and on cell type -highlighted terms receptor protein and skeletal muscle cell -complex, many types of receptors in same cell-ma |
| proliferation | rapid growth; spread; multiplication |
| example of receptors for cell signals inside cell membrane | steroid hormones, Hydrophobic (large) -receptors-in cytosol or nucleus -regulate gene transcription -hormone binding receptor conformation change -activation or inhibitation of transcription of particular proteins -hormones have specific receptors |
| vasodilation | widening of blood vessels |
| viagra | inhibits breakdown of cGMP by cGMP-specific phosphodiesterase type 5 longer NO effect vasodilation (purpose: increase blood flow in the body to tissues or organs that need it most (to meet local need of oxygen) |
| signaling cascade can amplify extracellular signals | -transform/transduce signal -relay signal from cell surface and (often) amplify/strengthen signal -sometimes can distribute signal to more than 1 type of cell response -modulate signal so cell responds to precise conditions |
| exogenous substances mimic signal molecules | often resemble natural signal molecules -occupy receptor binding site cell response, or bind receptor binding site natural signal prohibited from binding inhibit cell responses, or bind other site on receptor activate or inhibit cell response |
| cell membrane receptors | -receive most signals, many types of signal molecules, can enter cells directly -three families of signal receptor proteins 1.ion-channel-linked 2. G protein-linked and 3. enzyme-linked -many receptor types w/in families -some signal wk thr sev familie |
| molecular switch mechanisms | -impor to G pro and enz-linked receptors, most molecules in "relay" are proteins, switch from inact to act when recived, act prot in cascade -must be switched off to original cell state,cell uses phosphorylation to cause proteins to change conformation |
| enzymatic phosphorylation swithces | Kinase adds PO4 group, may activate or inactivate protein |
| phosphorylation by GTP binding | -important for g protein linked receptors -gtp bound to protein to activation. -inactivation by cleavage of PO4 from GTP to gdp bound to protein to reactivate, gtp replaces gdp |
| G-protein-linked receptors | largest family, respond to hormones, locally-released molecules, neurotransmitters, all receptors are seven pass transmembrane proteins |
| all receptors | are seven-pass transmembrane proteins |
| G proteins | general structure 3 subunits (alpha, beta, Y) 2 (alpha, Y)-short lipid tails embedded in cell membrane, when not stimulated, alpha bound to GDP, binding of signal molecule to receptor to conformational change in receptor, altered receptor activates G pro |
| G proteins cont. | alpha subunit releases GDP, Alph subunit binds with GTP, g protein dissociates , and both alph and beta/Y complex can interact w/target proteins in cell membrane |
| Switching off G protein subunits dependent on Alpha subunit | Has intrinsic GTPase activity, GTP->GDP, so subunit coverts to inactive form, inactive alpha subunit recombines w/beta/Y to fully associated inactive g protein reestablished. cyle describes on/off mechanism of switch some poisons work by distrupting switc |
| Pathway based on cAMP | some g proteins activate signal transduction pathways, common g protein linked pathway based on cAMP |
| adrenaline | cell responses mediated by cyclic amp this case affects the heart and causes glycogen breakdown. |
| cAMP | g proteins regulate adenylate cyclase, activation or inhibition if activation cAMP produced -cAMP commonly activates protein kinase A (PKA) -several reaction altered metabolism, gene transcription, secretion |
| what does kinase do? | several reactions: altered metabolism, gene transcription, secretion |
| enzyme-coupled receptors | transmembrane proteins, has catalytic function facing cytoplasm or complexes w/ enzyme in cytoplasm -signal molecules often proteins -important to growth, proliferation, differetiation, movement -common catalytic function: receptor tyrosine kinase (RTK |
| Receptor Tyrsine Kinase (RTK) | common catalytic function |
| enz-coupled receptor proteins | 1 pass through membrane unlike g protein coupled(7 pass,bind extracellular signal, but must dimerize w/ another receptor molecule bound to its signal molecule, now intracellular parts of receptors come in contact w/each other to acti of kinase activity |
| Common Pathway: MAP knases | work through ras protein, similar to g proteins (gtp needed to activate) important targets: activation of transcription factors, what are transcription factors and what do they do |
| Ras/MAP kinase and cancer | stimulation of cell proliferation, ras permanently switched on, like constant mitogen signalling, mutant ras to cell division stimulated w/ no mitogen signal to cancer, onocogenes- mutations in genes for Ras other similar proteins important in many cancer |
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