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81 Cards in this Set
- Front
- Back
Name three things that signals allow organisms to do
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-Allow organisms to respond to their environment
-help maintain homeostasis -provide the ability to control function(s) |
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What Is Needed For Signaling?
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Mechanism for Generation
A Signaling Molecule A Receptor Cellular messaging mechanism Biochemical pathway |
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Describe Endocrine signaling, give an example
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Long distance
Insulin |
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Describe Paracrine signaling, give an example
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Medium to short distance
Histamine |
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What is autocrine signaling?
give an example: |
When a cell signals itself
prostoglandin signaling |
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What are estrogens and androgens, steroids examples of?
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Nuclear hormone signaling
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Name some hormones involved in nuclear hormone signaling
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estrogens
androgens steroids |
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Name four types of receptors seen in signaling and describe their speed
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-Ligand-gated ion channel
very fast -GPCRs fast -Kinase-linked receptors slow -Nuclear receptors really slow |
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Do cells ever actually touch each other in order to signal?
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yes. Plasma membrane attached signaling. In the immune system.
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What is an autocoid?
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A locally-acting hormone
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Name at least 5 properties of a receptor
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Proteins with 1 or More (up to 5) Subunits
Transmembrane Proteins Extracelluar Ligand Binding Domain Intracelluar “Activation“ Domain May be an Ion Channel May or May Not Need to Interact With Other Membrane Proteins (Example - GPCRs vs guanylyl cyclase) Very High Specificity For Ligands (Kd’s from 0.1-10 nM) Ligand Binding Generates Different Types of Intracelluar Regulatory Events or “Second Message” |
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Name 4 main types of receptor
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Ionotropic
Metabotropic Kinase Based Nuclear |
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How might one detect a hormone receptor?
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With a binding assay
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What is the basic idea of ligand binding/response theory?
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Response is Proportional to Receptor Occupancy
L / (L + Kd) |
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What is a consequence of kinase cascades?
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Signal amplification
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What is significant about the fact that kinase cascades amplify signals?
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Response of the Cell Often Occurs at Lower Ligand Values than the Kd of Receptors
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What are the three main channel families?
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Ligand-gated ion
Potassium Sodium or calcium |
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What do voltage-gated cation channels generate?
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Action potentials
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What sort of channels are responsible for action potentials?
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Voltage gated cation channels
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what changes in proteins can drive signaling?
Give an example |
conformational and phosphorylation
calmodulin |
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How many transmembrane domains do gPCRs have?
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7
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What STRUCTURAL change does calmodulin provide an excellent example of?
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Conformation changes involved in activation
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What example of cytokine sigaling was given in class? (Garrison)
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Cytokine→Jak→Stat
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Give a generic cascade following a growth factor signal
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Growth Factor binds
Receptor dimerisation Autophosphorylation of tyrosine residues Docking of SH2 domain protein SH2 acts as a dock for activation of Ras (GTP→GDP) Ras is activated via GEF MAPKKK, MAPKK, MAPK Various transcription factors Gene transcription |
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Where (what domains—extracellular or membranous) do g-protein coupled receptor ligands bind?
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Both inside and outside the transmembrane helixes
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Describe a general GPCR/Adenylyl cyclase cascade
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Ligand binds to receptor, causes intracellular conformational change
Receptor acts as a GEF Heterotrimeric g-protein dissociates into alpha and beta-gamma subunits catalyzed by exchange of ADP for ATP Alpha (generally) binds to adenylyl cyclase at Switch II domain Cyclase activates synthesis of cAMP from ATP cAMP activates PKA PKA phosphorylates targets (not necessarily diffused, however. AKAPs act as scaffolds. |
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What are the three functions of AKAPs?
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Target PKA to site
Assemble signaling complexes that include substrate and phosphotase Reorganize complexes |
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What are scaffolds for PKC called?
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RACKs
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What does phosphorylation change and not change?
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Changes the activity (Km)
Does not change the maximum activity (Vmax) |
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Is a small amount of phosphorylation useful?
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Generally not. Stoichiometric phosphorylation is usually necessary to potentiate change
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Describe the action of pyruvate kinase
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SOMEBODY PLEASE FILL THIS IN
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Describe a general GPCR PLC cascade
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General steps involving receptor binding, GProtein conformational change
Alpha activates PLC PLC breaks down membrane-bound PIP2 into membrane bound DAG and cytosolic IP3 DAG activates PKC, PKC phosphorylates substrates IP3 translocates to the nucleus and frees calcium Calcium can do its work in the cell, such as gate channels, etc., activate calmodulin |
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Give a general description of calmodulin
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It is an intracellular Ca+ receptor
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What is the general pathway for receptor recycling?
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GRKs phosphorylate
Arrestins bind, stop signaling Receptor is internalized in a clathrin-bound vesicle It is either recycled and modified by phosphatases or ubiquitinated and sent to a lysozome for destruction |
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What is the main difference between Class A and Class B receptor recycling?
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Class A, rapid, nuclear translocation of pERK,
Class B, no nuclear translocation—however, cytosolic signaling via recruitment of other proteins |
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How is glycogen metabolism regulated by PKA and cAMP
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Reduce glycogen synthesis, increase glycogen breakdown, and increase lipolysis
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Name 4 ways Jak Stat can be inhibited
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Phospotases on Jaks
Competition for Tyr binding Ubiquitination of Jaks Modification of stats by PIAS |
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What is the general Jak/Stat pathway?
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Ligand binds to receptor
Receptors cross link Jaks cross-phosphorylate Jaks phosphorylate receptor tyrosines Stats associate to phosphorylated receptor Stats dimerize via SH2 domain Stat Dimer translocates to nucleus |
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Give the basic TGF-Beta pathway
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Type 2 receptor binds to ligand
Type 2 and 1 receptors dimerize and type 1 is phosphorylated by 2 Inhibitory Smads are kicked off Type 1 Smad 2 or 3 are phosphorylated by Type 1 receptor, unfold, dimerize with Smad 4 (mediated by SARA) Complex translocates to nucleus |
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How would the amplitude of a signal be regulated?
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Competition between pos and negative regulation
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What influences the duration of a signal?
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Induction of a negative signal
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What motif does SH3 bind?
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Proline-rich
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Give 2 examples of cross-talk
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Stats can be activated by Receptor Tyrosine Kinases.
TGF-B can activate MAP kinase via TAB-1 Ras/Map kinase signaling can inhibit Smad nuclear accumulation |
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Opposing and cooperative effects of TGF-B and Ras signaling: Give tissue examples
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Epitheleial cells: antagonistic
Fibroblasts: cooperative |
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Give an example of nuclear cross-talk
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GFAP expression is activated by BMP and LIF
Smads and STATs are required for full activity The p300 coactivator integrates these two signals Or just, p300 coactivator integrates Smads and STATs |
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What motif does a Pleckstrin homologous site bind?
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PIP2, 3
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Name 4 mechanisms employed to transmit signals
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Kinases (phosphatases)
Creation of protein docking sites Removal (proteolysis) of regulatory proteins Regulation of localization |
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Are SH2 domains specific?
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Yes
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How does hedgehog work in the case of cubitus interuptus?
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Patched naturally inhibits smoothened receptor
Hedgehog deinhibits smoothened by activating patched Proteolyzed form of Ci is a repressor Hedgehog signaling inhibits proteolysis of Ci Full-length protein activates transcription |
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How can hedgehog signal to distant cells?
How was this tested? |
Precursor SHH is cleaved into a membrane-tethered form and a “free” form
Free form is able to diffuse in a gradient Tested by use of conditioned media from SHH transfected cells |
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How does Protein kinase B (Akt) inhibit apoptosis? (In brief)
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PI3 kinase activates PKB which inhibits the activation of the procaspase 9 – caspase 9 – procaspase 3 – caspace 3 apoptotic cascade
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Name two ways to identify receptors
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Affinity chromatography
Affinity labeling |
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How do PDGF, FGF and Eph RTKs bind receptors and what is the commonality?
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PDGF: Ligand dimerizes
FGF: FGF is bound to proteoglycan Eph: Eph receptors dock via ligand for bidirectional signaling Commonality: dimerization of receptors |
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What motif does SH2 bind?
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Phosphotyrosine
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What is Smad 4 required for?
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DNA binding, transcriptional activation
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What is Smad 4 not required for?
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Receptor interaction, nuclear translocation
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What does Smad 6 do?
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Competes with Rsmads
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What does Smad 7 do?
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Blocks Rsmad phosphorylation
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What does inhibin do?
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Competes with ligand for TGF-B binding
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Shup:What is the purpose of the AB region of the nuclear receptor?
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Phosphorylation sites. Bind cytoplasmic molecules
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Shup:What is the purpose of the C region of the nuclear receptor?
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DNA binding
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Shup:What is the purpose of the D region of the nuclear receptor?
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This is the hinge region
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Shup:What is the purpose of the E region of the nuclear receptor?
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Ligand binding
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Shup:What two regions minimally confer the entire function of a nuclear receptor molecule?
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C and E. DNA binding and Ligand binding
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Shup:What two areas are responsible for Nuclear localization?
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D and E (hinge and ligand binding)
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Shup:What is the part of a receptor that varies the most?
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The N-terminus
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Shup:Where is the most homology in nuclear receptors?
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The DNA binding domain
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Shup:What are two important regions found in the Zn fingers?
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The D-box (dimerization) and P-box (DNA binding)
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Shup:Which box is diagnostic for the type of receptor?
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The P-box
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Shup: What are the two main types of hormone response elements that are involved in DNA binding?
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Palindromic and direct repeat
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Shup: What is RXR?
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It is a critical protein that forms dimers with direct repeat receptors.
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Shup: What three receptors form heterodimers via direct repeats and RXR?
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RAR, Vitamin D, Thyroid receptor
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Shup: How do steroid receptors bind?
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Homodimers with palindromic sequences
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Shup: What sort of mutants often lead to no transcription?
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Ligand or DNA binding. Dominant negative phenotype. Sequester wildtype.
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Shup: Explain CHIP
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Use formaldehyde to fix DNA + complexes
Shear DNA Unfix Immunoprecipitate with antibodies |
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Shup: What are 2 ways that corepressors work?
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Prevent recruitment of coactivators
Have HDAC activity Physically block activators |
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Shup: What is one way receptor antagonists do what they do?
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Recruit co-repressors. Tamoxifen is a good example.
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Shup: What is the AF-2 region critical for?
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Transcriptional activation
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Shup: Explain the importance of proteosome activity
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In the absence of proteosome, there is no receptor cycling, transcription stops
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Describe the RTK to Ras pathway for EGF
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RTK binds ligand--2 ligands, 2 receptors
receptors dimerize receptors phosphorylate each other at tyrosine residues association with Grb-2 (has SH2 and SH3 domains) Grb-2 binds Sos, Sos acts as GEF for Ras Ras covers inacivation domain of Raf -->Mek, Erk, transcription factors |
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Describe the AKT (PKB) pathway
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PI3 Kinase
PIP2 to PIP3 PDK1, AKT BIND TO PIP3 PDK1 activates PKB (AKT) With ligand, inhibits apoptosis via caspase regulation without ligand, apoptosis |