Ch 35 Lecture 1

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Ch 35 Lecture 1
2014-11-09 22:31:23
Test Three
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  1. Most molecular motor protiens are members of the __. 
    What are blast cells? 

    How do you induce differentiation?
    P loop NTPase family

    still capable of dividing and proliferating

    Adding a differentiaiton signal, such as MyoD, which signals production of transcription factors, which deactivate genes for proliferation and activate muscle specific protiens. They fuse together cell contents within cells.
  2. Explain a sarcomere.
    nuclei migrate to the periphery and control a function of the cell

    several in a single muscle fiber

    it is the functional unit; gets smaller upon contraction
  3. What are the two proteins in the sarcomere?
    • actin: filamentous structural protein; cells form long thin fibers
    • myosin: mechanoenzyme; member of P-loop ATPase family; uses enzymatic activity to do mechanical work; thicker than actin

    actin and myosin overlap in the A band
  4. What are the theories of contraction?
    thy can ball up 

    or they can slide relative to each other
  5. What experiment did they do to test the relationship with actin and myosin?
    took a beaker with actin and a beaker with myosin and poured them together

    the solution became viscous because they were bonding. 

    Took the viscous solution and added ATP--> viscosity went down because ATP allowed a reaction between actin and myosin to reverse itself
  6. What is the cycle between actin, myosin, and ATP?

    ATP displaces actin--> ATP-myosin

    Hydrolysis of ATP: ADP-P-Myosin

    Actin attaches: Actin-ADP-P-Myosin

    ADP-P leaves: Actin-Myosin
  7. Second experiment?
    myosin in buffer; add ATP; observe conformational changes
  8. Third experiment performed

    And result of this
    cleaved using papain and trypsin: 

    got four segments

    S1 and S2, the globlar heads

    • HMM: contains the S1 and S2 domains
    • LMM: forms the alpha helical coiled coil. This coil has no kinks (no proline); there's a repeat of seven amino acids; less mass
  9. What do trypsin and papain do myosin? What is the original structure of myosin? 

    what do the globular heads do?

    What does the Ploop do?
    Trypsin separates the LLMM from the HMM

    myosin: 520 kD molecule made of 6 polypeptide chains

    papain separates the active site from the other chain

    ATPase activity limited to globular domain; doesn't form filaments, but hydrolyzes ATP

    Ploop has sequence that allows ATP to move out
  10. Explain in detail the seven repeating amino acids.

    • A and D: hydrophobic
    • BCF: charged

    A and D always end up on the same side, allowing them to hide  in the helix; hyrophobic interactions allow tighter binding

    The charged ones lie outside.
  11. What does the neck region of myosn consist of?
    the essential and regulatory lght chains, whcih reinforce and give strength during conformational changes
  12. Myosin is a __ moleule with ___ and __.

    • + end being the heads
    • - ends being the tails
  13. How does actin exist?
    as individual subunits called g actin (globular actin)

    g actin polyerizes into a filament--> F actin, which is an ATPase, but doesn't use it to do work. It uses it to help polymerize

    It is also unidirectional and polar
  14. What is the optical trap experiment?
    • there are beads that a laser beam can monitor the movement/ distance of and a thin filament stretched over the beads (ceramic)
    • there is a middle bead that has the HMM

    ATP is added and actin begins to hydrolyze it; the beads move in stepwise fashion due to myosin pushing along actin in stepwise fashion
  15. What effect does ATP binding have on myosin?

    What effect does ATP hydrolysis have?
    it decreases it's affinity for actin, causing it to let go and undergo a conformational change

    affinity for actin increases; binds in a new place and release of inorganic phosphate
  16. What are the two different conformations?
    Myosin's lever arm has two conformations depending on whether ATP is bound or absent.

    When ATP is bound, the lever arm reorients itself, performing a power stroke.
  17. Explain what a small movement in the P loop region can do.
    P loop attaches to switches, which attach to relay helix, which attach to lever arm

    A little movement in the P loop translates into slightly larger movement in the swtich 1 adn slightly larger change in switch II, relayed to relay helix, movement of lever arm.
  18. How is the myosin and actin association controlled?
    tropomyosin and the troponin complex; 

    tropomyosin wraps around actin, covering the binding site and preventing myosin from bindning.
  19. Explain in detail the troponin complex.
    It has the TnC, TnI, and TnT regions

    TnT is a tropomyosin-binding subunit which regulates the interaction of troponin complex with thin filaments;

    • TnI inhibits ATP-ase activity of acto-myosin;
    • TnC is a Ca2+-binding subunit, playing the main role in Ca2+ dependent regulation of muscle contraction
  20. Explain muscle contraction in terms of action potential.
    • in cells, the SR is where calcium is sequestered. 
    • Action potential depolarizes cells, causing a release of Ca, which binds to TnC subunit of the troponin complex

    TnC changes conf

    TnI changes conf, moving tropomyosin away and revealing a binding site that myosin can now access
  21. Why is the cytoskeleton complex?
    • gives structure to cell with no cell wall
    • railway or communication system/ cell unit
  22. Since everything is connected, we can do what?
    send info and elements and move things in the cell
  23. What are the components of the cytoskeleton?
    microtubules: made of alpha and beta tubulin, whcih polymerize to form a hollow tube with a hollow core

    microfilaments: made of actin

    intermediate filaments: made of keratin; comes together in multisubunit helices like collagen
  24. Why are microtubules directional?
    they have a plus and minus end; organized at the microtubule organizing centers; binding of the first subunit allows polymerization outward
  25. What is the motivation to assemble and disassemble?

    • GTP in active site--> polymerization
    • GDP: depolymerization
  26. Eukaryotic flagella are anchred by __. Explain it.
    axoneme; bundle of microtubule fibers adn other associated fibers that is continuous with the membrane; there is a nine plus two aray, and subfiber A is continuous; subfiber B is not
  27. __ is the __, located all the way up and down the flagella. 
    __ connects pairs of microtubules together. Everything in an axoneme must __.
    • dynein
    • ATPase
    • nexin
    • stay connected
  28. Explain dynein
    • multiple binding sites for ATP
    • gets ATP in the active site; reaches out to next microtubule to grab on; hydrolyzes ATP--> conformational change that allows the power stroke to occur
  29. What are three facts about dynein?
    it is an ATPase

    uses energy associated with hydrolysis to do work

    has an affinity for MT; and, that affinity changes whether ATP or ADP is bound
  30. As dynein walks along the microtubule, what do the microtubules do? How about when dynein is released?
    • they bend relative to each other
    • they spring back
  31. Explian the structure of kinesin.
    fairly large protein with four subunits; globular motor domain; large helical coiled coil domain

    different from myosin in that the binding site for vesicles is the tail
  32. Explain the optical trap experiment using kinesin?
    • single kinesin bound to a ceramin bead
    • substrate kinesin walks on is a MT from teh minus end to the plus end

    Over time, bead was displaced in stepwise fashion.
  33. What does kinesin have?
    it has a ploop, switch I and II, relay helix attached to neck linker

    small changes in the middle lead to a big change outside
  34. similarities between myosin and kinesin

    use atp to hydrolyze bond--> eergy converted into conformational change--> work

    proteins bound to MT not actin; subtle difference in attaching

    • in kinesin: ATP bound leads to greater affinity for actin
    • in myosin: ATP bound leads to release
  35. Bacterial flagellar motion
    counterclockwise rotation allows swimming
  36. Explain bacterial flagella
    made of protein called flagellin; comes together to form hollow tube; the flagellum rotates--> different motor and energy source: proton gradient
  37. Flagella is anchored by __; come throguh __ and anchors self in _, which is made of __.
    • rod
    • rings
    • MS ring
    • FliG
  38. Which has lower pH, MotA or MotB?
    Mot B thanks to pumps that pump protons out of cell
  39. Explain MOtA and MOtB
    one is a half channel taht connects to outside of membrane (MotA) and one connects inside (MotB); they get halfway; and FLiG allows acces to other half channel
  40. Explain the rotation
    proton hops to ms ring, spins around in counterclockwise direction; goes to other channel