# Bacterial Flagellum (DD-559)

> 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.

- Department: Science (also Nature)
- First published: 2025-05-01
- Last updated: 2025-05-01
- Permalink: https://detailenjoyer.com/case/bacterial-flagellum/
- Author: Marcus Easterling (DetailEnjoyer), The Detail Department

## Quick facts

- **DD-559-F01**: Rotary motor. _(Write-up · Exhibit A (Type))_
- **DD-559-F02**: Proton or sodium flow. _(Write-up · Exhibit B (Power))_

## Write-up

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

1. **Type**: Rotary motor.
2. **Power**: Proton or sodium flow.
3. **Action**: Spins like a propeller.
4. **Run**: Forward swimming.
5. **Tumble**: Reorients.

## Related case files

- [Bacteria Hunters (DD-309)](https://detailenjoyer.com/case/bacteria-hunters/): I linked more on bacteria

## Reel vs. record

- **Note**: None needed.

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

- Duration: 20.2 s · Published: 2025-05-01
- File: https://detailenjoyer.com/assets/videos/DJGkIL2RzuI.mp4

### Transcript

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!

## Questions & answers

**Q: Motor type?**  
A: Spins. _(Source: Write-up · Exhibit A (Type) · Wikipedia: Flagellum)_

**Q: Power source?**  
A: Protons. _(Source: Write-up · Exhibit B (Power) · Wikipedia: Flagellum)_

**Q: Run vs tumble?**  
A: Direction. _(Source: Write-up · Exhibit C (Action) · Wikipedia: Flagellum)_

**Q: Where is the motor?**  
A: Envelope. _(Source: Write-up · Exhibit D (Run) · Wikipedia: Flagellum)_

**Q: Shape of filament?**  
A: Flagellum. _(Source: Write-up · Exhibit E (Tumble) · Wikipedia: Flagellum)_

## Sources

- [Wikipedia: Flagellum](https://en.wikipedia.org/wiki/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/