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
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
- helical structure that has 5.5 subunits per turn
- 11 protofilaments
§ each flagellum has a __; and they form not by __ but, instead, by the __.
· Each flagellum is __; and, at its base, each flagellum has a __
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
__ drives __; __is not required
The necessary free energy is derived from the __ that exists across the plasma membrane.
The flagellar motor is complex with __
- Proton flow
- bacterial flagellar rotation
- proton gradient
- 40 distinct proteins
Five components crucial to motor function have been identified
- · 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
FliG, FliM, and FliN are part of a __ called the __, with about __ coming together to form __.
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
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.
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.
Bacterial chemotaxis depends on the __
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
- coherent bundle
- intrinsic shape of each filament
- swims smoothly
- flies apart
- screw sense of the helical flagella does not match the direction of rotation
- pulls in a direction
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
- swimming for longer periods of time without tumbling when moving toward higher concentrations of it
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
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
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
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
- releases its phosphoryl group
- phosphorylated CheY
- less likely to rotate in a clockwise direction
- reversible rotary flagellar motor
- phosphorylation-based signaling pathway
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