Chapter Text 35.4

  1. ·         In the bacterial motor, __ rather than __. The direction of rotation can change rapidly, a feature that is central to __, the process by which bacteria swim preferentially toward an increasing concentration of certain useful compounds and away from potentially harmful ones
    ·         Bacteria swim by rotating flagella that lie on their surfaces. When the flagella rotate in a counterclockwise direction, the separate flagella form a bundle that very efficiently propels the bacterium through solution
    • an element spins around a central axis
    • moving along a polymeric track
    • chemotaxis
  2. o   Bacterial flagella are polymers approximately __ in diameter and as much as __ in length, composed of a protein called __
    §  These subunits associate into a __, giving the appearance of __

    • 15 nm
    • 15 micrometers
    • flagellin
    • helical structure that has 5.5 subunits per turn
    • 11 protofilaments
  3. § each flagellum has a __; and they form not by __ but, instead, by the __.

    · Each flagellum is __; and, at its base, each flagellum has a __
    hollow core

    growing at the base adjacent to the cell body

    addition of new subunits that pass through the hollow core and add to the free end

    twisted in a left-handed sense

    rotory motor
  4. ·         __ drives __; __is not required
    o   The necessary free energy is derived from the __ that exists across the plasma membrane.
    o   The flagellar motor is complex with __
    • Proton flow
    • bacterial flagellar rotation
    • ATP 
    • proton gradient
    • 40 distinct proteins
  5. §  Five components crucial to motor function have been identified
    • MotA
    • MotB
    • FliG
    • FliM
    • FliN
  6. MotA

    • ·         MotA: membrane protein that has four transmembrane helices and a cytoplasmic domain
    • ·         MotB: membrane protein with a single transmembrane helix and a large periplasmic domain
    • o   11 MotA-MotB pairs form a ring around the base of the flagella
  7. ·         FliG, FliM, and FliN are part of a __ called the __, with about __ coming together to form __.
    o   The 3D structure of the __ of FliG reveals a __ with a set of charged amino acids, conserved among many species, lying along the thick edge of the wedge
    • disc-like structure
    • MS (membrane and supramembrane) ring
    • 30 FliG subunits
    • a ring
    • carboxyl terminal half
    • wedge-shaped domain
  8. o   The __ and __ combine to create a __ that drives the __. How?

    • MotA-MotB pair and FliG
    • proton channel
    • rotation of the flagellum.

    §  Each MotA-MotB pair is conjectured to form a structure that has two half-channels; FliG serves as the rotating proton carrier, perhaps with the participation of some of the charged residues identified in crystallographic studies.
  9. Explain the scenario
    • ·         In this scenario, a proton from the periplasmic space passes into the outer half-channel and is transferred to an FliG subunit.
    • ·         The MS ring rotates, rotating the flagellum with it and allowing the proton to pass into the inner half-channel and into the cell. 
  10. ·         Bacterial chemotaxis depends on the __
    o   Bacteria swim in one direction for some time, tumble, and go in a new direction
    §  Tumbling is caused by __
    ·         When rotating __, the helical filaments form a __ favored by the __, and the bacterium __
    ·         When the rotation reverse (__), the bundle does what because the what?. Each flagellum then __ and the cell __.
    • reversal of the direction of flagellar rotation
    • reversal of the direction of the flagellar motor
    • counterclockwise
    • coherent bundle
    • intrinsic shape of each filament
    • swims smoothly

    • clockwise
    • flies apart
    • screw sense of the helical flagella does not match the direction of rotation
    • pulls in a direction
    • tumbles
  11. o   In the presence of a gradient of certain substances like glucose, bacteria swim __; these are __. On the other hand, bacteria migrate away from harmful compounds, called __
    §  This movement in response to environmental cues is __
    ·         Chemoattratants cause what?
    ·         __is more frequent when moving toward lower concentrations of the chemoattractant
    • toward the direction of higher concentration
    • chemoattractantts
    • chemorepellants
    • chemotaxis
    • swimming for longer periods of time without tumbling when moving toward higher concentrations of it
    • Tumbling
  12. §  This behavior is reversed for chemorepellants
    §  The result of these actions is a __ that facilitates net motion toward conditions more favorable to the bacterium
    biased random walk
  13. o   Chemotaxis depends on a __ that terminates at the __.
    §  The signaling pathway begins with the __.
    ·         In their unoccupied forms, these receptors __leading eventually to the __
    • signaling pathway
    • flagellar motor
    • bidnign of molecuels to receptors in the plasma membrane
    • initiate a pathway 
    • phosphorylation of a specific aspartate residue on a soluble protein called CheY
  14. o   In its phosphorylated form, CheY __. When bound to phosphorylated CheY, the flagellar motor __
    • binds to the base on the lgellar motor
    • rotates in a clockwise rather than a counterclockwise direction, causing tumbling
  15. o   The binding of a chemoattractant to a surface receptor __. Phosphorylated CheY spontaneously __ and __ in a process accelerated by another protein, __.
    §  The concentration of __ drops, and the flagella are __. Under these conditions, bacteria swim smoothly without tumbling
    §  Thus, the __ and a __ work together to generate an effective means for responding to environmental conditions
    • blocks the signaling pathway leading to CheY phosphorylation
    • hydrolyzes
    • releases its phosphoryl group
    • CheZ
    • phosphorylated CheY
    • less likely to rotate in a clockwise direction
    • reversible rotary flagellar motor
    • phosphorylation-based signaling pathway
  16. ·         Bacteria sense __ by measurements separated in time
    It sets off in a random direction and, if the concentration of the chemoattractant has increased after the bacterium has been swimming for a period of time, what happens?
    • spatial gradients of chemoattractants
    • the likelihood of tumbling increases and the bacterium tests other random directions
Card Set
Chapter Text 35.4
Test Three