Ch 3 Flagella
In a peritrichous bacterium, the flagella are all
bundled together in a very streamlined way, allowing for efficient movement.
Bacteria achieve directional movement by
changing the rotation of their flagella.
When tumbling, flagella are splayed out while rotating in a
clockwise direction, creating a looping motion and reorienting the cell toward the direction of the attractant.
Without a chemical gradient, flagellar rotation cycles between
counterclockwise (run) and clockwise (tumble) with no overall directional movement.
When running, flagella rotate in a
counterclockwise direction, allowing the bacterial cell to move forward.
Gram-positive and gram-negative bacteria have different basal body configurations due to
differences in the cell wall structure
Axial filaments of bacterial are also called
endoflagella
Bacteria can move in response to a variety of environmental signals, including
light (phototaxis), magnetic fields (magnetotaxis) using magnetosomes, and, most commonly, chemical gradients (chemotaxis).
A bacterium with a singular flagellum, typically located at one end of the cell (polar), is said to have a
monotrichous flagellum.
When an attractant exists, runs and tumbles still occur; however, the length of runs is longer, while the length of the tumbles is reduced, allowing
overall movement toward the higher concentration of the attractant.
Flagella that cover the entire surface of a bacterial cell are called
peritrichous flagella
Bacterial flagella act like
propellors
When no chemical gradient exists, the lengths of runs and tumbles are more equal, and overall movement is more
random
In a cell with peritrichous flagella, the flagella bundle when they rotate in a counterclockwise direction, resulting in a
run.
Endoflagells is found in
spirochetes (this means flagella is on each cide)
Flagella are
stiff spiral filaments composed of flagellin protein subunits that extend outward and spin in solution
Flagella
structures used by cells to move in aqueous environments
Purposeful movement toward a chemical attractant, like a food source, or away from a repellent, like a poisonous chemical, is achieved by increasing
the length of runs and decreasing the length of tumbles.
However, when a chemical gradient of an attractant exists,
the length of runs is extended, while the length of tumbles is decreased.
The basal body of flagella is
the motor and is embedded in the plasma membrane
Cells with lophotrichous flagella have a
tuft at one end of the cell.
However, when the flagella rotate in a clockwise direction, the flagella are no longer bundled, resulting in
tumbles.
chemotaxis
an overall directional movement toward the higher concentration of the attractant
Endoflagella is
anchored at one end of a cell, and rotation causes the cell to move
The basic structure of a bacterial flagella consists of
a basal body, hook, and filament
Cells with amphitrichous flagella have
a flagellum or tufts of flagella at each end.