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Lecture 14

Lecture 14 - Chapter 15&16 - March 5.docx

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York University
BIOL 2021
Patricia Lakin- Thomas

March 5, 2013 Part 2: Chapter 16 – Cytoskeleton Part 1: From Elisa Cell Signaling: Chapter 15  Know figure 15-66  Receptor Tyrosine Kinases (RTKs) o How do we inactivate/ turn off the signal?  Protein tyrosine phosphatases remove phosphates from tyrosines  Specific for substrate  Time + place of action can be regulated  Serine/ Threonine Kinases  Receptors are similar to RTKs as they are both transmembrane proteins in plasma membrane  Ligands= extracellular proteins (called transforming growth factor-beta, TGF-beta)  Many proteins- superfamily  Act as hormones or local mediators  All are dimeric proteins  Figure 15-69  Dimeric ligand will bring together receptors--> “Smad” protein o Receptors are heterodimers (different from each other)  They transphosphorylate each other which activates them  Activated receptor has kinase activity and will phosphorylate Smad proteins  Smad= gene regulatory protein  Will enter nucleus and affect gene transcription, important to development and tissue repair etc.  Quick route to nucleus (not as quick as a nuclear receptor, but very quick for an extracellular protein)  Why so complicated?  Cells integrate and compute information (they get signals from many sources and will have to decide what to do)  Quantitative interactions between signals not just qualitative on/off response  We can use computer models to understand cells Histidine Kineses  Histidine-kinase associated receptor  Actual receptor does not have kinase activity, but it will activate one downstream  Two-component signaling pathways used by bacteria, yeast, plants NOT IN ANIMALS  E.coli: bacterial chemotaxis o Movement towards an attractant (some sort of chemical) or away from a repellant o Figure 15-71a (E.coli flagella moves COUNTERCLOCKWISE (very important) o Figure 15-72 o All rotors counterclockwise = swim smoothly o Some rotors reverse-->clockwise= random tumbling, no forward movement o Bacteria switch back and forth between these o After tumbling: move forward in a new random direction o Bacteria cannot turn corners o What’s the point?  Tumble randomly, find a new direction and see if this is better  They continue smooth swimming if the direction is favorable  If not, they tumble and try again  Figure 15-71  Rotor drives flagellum  Rotates counterclockwise  Figure 14-17  H+ flowing inside drive rotor  Stator= part of basal body in peptidoglycan layer and is stationary  Rate of tumbling low= things are good, high rate= things are bad, trying to find a better way  Control rate of tumbling:  2-component signaling  Chemotaxis receptor= transmembrane protein  Binds both attractants and repellants  Figure 15-73  CheW= adaptor protein= binds CheA to receptor  CheA= histidine kinase
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