Ch 9.4

Card Set Information

Ch 9.4
2014-10-11 11:14:06
Test Two
Show Answers:

  1. ·         These enzymes catalyze the __ and use the energy associated with this thermodynamically favorable reaction to drive the __
    • hydrolysis of ATP to form ADP and Pi
    • motion of molecules within cells
  2. Structure
    ·         Structure: elongated structures with globular domains that actually carry out ATP hydrolysis

    • o   Single globular domain with 750 amino acids; water-filled pocket at center of structure, suggesting possible nucleotide-binding site
  3. o   Conformational changes are amplified by other structures in the elongated myosin molecules to __ or other cargo substantial distances within cells

    transport proteins
  4. ·         ATP hydrolysis proceeds by the attack of water on the __
    ·         These enzymes are __in the absence of __but acquire activity on the addition of these ions
    o   The metal is not a component of the __. Rather, __bind these ions, and it is the __ complex that is the true substrate for the enzymes
    §  __ are the true substrates for essentially all __
    gamma phosphoryl group

    • inactive
    • divalent metal ions like Mg2+ and Mn2+ 

    • active site
    • nucleotides 
    • metal ion-nucleotide

    • Magnesium or manganese complexes of nucleoside triphosphates
    • NTP-dependent enzymes
  5. ·         There is no __ in an appropriate position and the__ is too far away from the __to play this role
    ·         Formation of the transition state for ATP hydrolysis is associated with a __
    • basic residue
    •  Mg2+ ion
    • phosphoryl group 

    substantial conformational change
  6. o   The catalytically competent conformation of the myosin ATPase domain must do what?
    §  ATP hydrolysis includes a __, which was determined to be the case with __
    ·         Vadium forms similar structures. When the structure was crystallized, it was shown to have a complex that matched the expected TS structure, with __
    bind and stabilize the transition state of the reaction

    • pentacoordinate transition state
    • TS analogs
    • vanadium coordinated to five oxygens
  7. o   The __ is coordinated to one oxygen from the __, __, __, and __. But, the ion doesn’t directly play a role in __
    §  An additional residue from the enzyme, __, is well positioned to play a role in catalysis
    • Mg2+
    • vanadate
    • one oxygen from ADP
    • two hydroxyl groups from the enzyme,
    • two waters
    • activating the attacking water
    • serine
  8. ·         In the proposed mechanism of __, with the __facilitating the transfer of a proton from the attacking water to the __, which, in turn, is deprotonated by one of the oxygen atoms of the __.
    Thus, in effect, the ATP does what?
    • ATP phoryl group
    • hydroxyl group of serine 
    • hydroxyl group of serine
    • gamma-phosphoryl group
    • serves as a base to promote its own hydrolysis
  9. ·         Difference between myosin ATPase domain complexed with ATP versus ADP-vandate
    o   A stretch of amino acids moves closer to the nucleotide by 2 angstroms and interact with the oxygen atom that corresponds to the attacking water molecule. These changes help facilitate the hydrolysis reaction by stabilizing the TS, but there are even more striking changes
  10. ·         A region comprising approximately __  at the __ of the domain adopts a different configuration in the __, displaced by 25 angstroms from its position in the ATP complex
    o   This displacement does what? and the effect is amplified even more as the __ is connected to other structures within the elongated structures typical of myosin molecules 
    • 60 amino acids
    • carboxyl-terminus
    • ADP-vanadate complex
    • amplifies the subtle changes in the active site
    • C-terminal domain
  11. §  Thus, the conformation that is capable of __ is substantially different from other conformational changes that take place in the course of the catalytic cycle
    promoting the ATP hydrolysis reaction
  12. ·         Why are myosins slow?
    o   The structure of the TS is __. Many of the interactions that stabilize the transition state will help __
    §  Thus, the equilibrium constant between enzyme-bound reactants and products is often close to 1, regardless of the equilibrium constant for the reactants and products free in solution
    Because each molecule of ATP is cleaved to ADP and Pi and then reformed from these products several times before the products are released

    intermediate between the enzyme-bound reactants and the enzyme-bound products

    equalize the stabilities of the reactants and the products
  13. ·         The hydrolysis of ATP to ADP and Pi is not the __, but the __is. The fact that a conformation of myosin with ATP hydrolyzed but still bound to the enzyme persists for a significant period of time is critical for __
    • RLS
    • release 
    • coupling conformational changes that take place in the course of the reaction to other processes
  14. ·         In myosins, a __is present, which consists of a __, surrounded on both sides by __
    o   Between the beta strand and the first helix is a __. This is the __because it interacts with phosphoryl groups on the bound nucleotide
    • conserved NTP-binding core domain 
    • central beta sheet
    • alpha helices

    • loop that has several glycine residues that are often conserved between more closely related members of this large and diverse family
    • P-loop
  15. ·         The wide utility of __ domains is best explained by their ability to undergo substantial conformational changes on __ and __
    • P-loop NTPase
    • nucleoside triphosphate binding and hydrolysis