Wize University Biology Textbook > Cell Structure
Motor Proteins: Cilia and Flagella
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Motor Proteins
Motor proteins are a class of proteins capable of moving along a surface. In the cell, motor proteins move along components of the cytoskeleton and transport cellular components throughout the cytoplasm. The energy for their movement comes from ATP. Examples:
- Kinesin: moves along microtubules in the (+) direction.
- Myosin: moves along actin filaments.
- Dynein: moves along microtubules in the (-) direction.
The Three Types of Movement
1. Motor proteins "walk" along the cytoskeleton transporting cargo
- Head proteins attach to the cytoskeleton;
- Tail proteins attach to the cargo;
- The head proteins alternate attaching and detaching from the cytoskeleton, taking "steps" forward every time they re-attach.
2. Motor proteins cause a filament to move
- Head proteins attach to a filament (e.g. actin filament);
- Tail proteins are anchored to a surface;
- As the head proteins carry out "walking motion", the tail remains anchored. The head proteins therefore push the filament along, causing it to move.
3. Motor proteins cause a "bend"
- Tails attached to one microtubule;
- Heads attached to another microtubule;
- The two microtubules are held together by a linking protein;
- As the heads carry out their "walking" motion, it causes a bend to form.
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Cilia & Flagella
- Cilia and flagella are composed largely of microtubules, and move through the action of dynein.
- Composed of a 9 + 2 arrangement: 9 fused pairs of microtubules surrounding 2 central microtubules.
Cilia
Cilia are hair-like structures that protrude from the plasma membrane of many eukaryotic cells. Cilia beat in a whip-like fashion to move fluid across the cell surface; some protists use cilia for locomotion.
Example: some cells of the lungs have cilia.
Flagella
Flagella are similar in structure to cilia, but longer; their main role is in locomotion.
Practice: Dyneins and Kinesins
Dyneins and kinesins are associated with which component of the cytoskeleton?
Practice: Cilia and Flagella
What type of proteins make up flagella and cilia?