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Bacterial Flagellum

Short answer: The bacterial flagellum is a whip-like filament driven by a rotary motor at its base, embedded in the cell envelope. The flow of ions, typically protons or sodium ions, across the membrane turns the motor, spinning the filament like a propeller.

Counterclockwise rotation bundles the flagella so the cell runs forward; switching to clockwise makes it tumble and reorient. The footage, credited to Smart Biology, shows an animation of the flagellar motor.

VideoWrite-up1 sources
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What should you know about Bacterial Flagellum?

Quick facts. Each one stands alone and has a stable ID you can cite.

  1. Rotary motor.

    DD-559-F01 · Write-up · Exhibit A (Type)

  2. Proton or sodium flow.

    DD-559-F02 · Write-up · Exhibit B (Power)

Video transcript: Bacterial Flagellum: Many Bacteria Swim Using a Spinning Molecular Motor

Did you know the bacterial flagellum moves through a rotary motor mechanism powered by the flow of ions, typically protons or sodium ions, across the bacterial cell membrane. This ion flow drives the protein complex at the flagellum's base, causing the flagellum to rotate like a propeller. Depending on the direction of rotation, the bacterium can move forward or run or tumble to reorient itself. NOW YOU KNOW!

Burned-in captions, read frame by frame (see transcript.md) · 20.2s Reel ·

Video coming soonBacterial Flagellum · Instagram Reel
Bacterial Flagellum: Many Bacteria Swim Using a Spinning Molecular Motor Instagram Reel · · 20.2s

The write-up

Many bacteria swim using a spinning molecular motor. Ion flow across the membrane powers it.

  1. Exhibit A

    Type

    Rotary motor.

  2. Exhibit B

    Power

    Proton or sodium flow.

  3. Exhibit C

    Action

    Spins like a propeller.

  4. Exhibit D

    Run

    Forward swimming.

  5. Exhibit E

    Tumble

    Reorients.

Questions people ask about Bacterial Flagellum

Motor type?

Spins.

Source: Write-up · Exhibit A (Type) · Wikipedia: Flagellum

Power source?

Protons.

Source: Write-up · Exhibit B (Power) · Wikipedia: Flagellum

Run vs tumble?

Direction.

Source: Write-up · Exhibit C (Action) · Wikipedia: Flagellum

Where is the motor?

Envelope.

Source: Write-up · Exhibit D (Run) · Wikipedia: Flagellum

Shape of filament?

Flagellum.

Source: Write-up · Exhibit E (Tumble) · Wikipedia: Flagellum

Test Your Knowledge

All quizzes →

5 questions, all from this case file. Answers are revealed instantly.

  1. Motor type?

    1. Rotary
    2. Piston
    3. Jet
    4. Spring
    Show the answer

    Answer: A. Rotary Spins. Source: Write-up · Exhibit A (Type) · Wikipedia: Flagellum

  2. Power source?

    1. Ion flow
    2. Sunlight
    3. Sugar burning in the filament
    4. Magnetism
    Show the answer

    Answer: A. Ion flow Protons. Source: Write-up · Exhibit B (Power) · Wikipedia: Flagellum

  3. Run vs tumble?

    1. Changing rotation
    2. Changing color
    3. Splitting
    4. Growing
    Show the answer

    Answer: A. Changing rotation Direction. Source: Write-up · Exhibit C (Action) · Wikipedia: Flagellum

  4. Where is the motor?

    1. At the base
    2. At the tip
    3. In the nucleus
    4. Outside the cell
    Show the answer

    Answer: A. At the base Envelope. Source: Write-up · Exhibit D (Run) · Wikipedia: Flagellum

  5. Shape of filament?

    1. Whip-like
    2. Square
    3. Flat
    4. Spherical
    Show the answer

    Answer: A. Whip-like Flagellum. Source: Write-up · Exhibit E (Tumble) · Wikipedia: Flagellum

Cite this case file

Easterling, Marcus. "Bacterial Flagellum." The Detail Department (DetailEnjoyer), case file DD-559, last updated May 1, 2025. https://detailenjoyer.com/case/bacterial-flagellum/

Permalink: https://detailenjoyer.com/case/bacterial-flagellum/ · Last updated

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