33. Cillia and Flagella

Question 1

Cilia and Flagella?

Answer 1

Function

• Cilia and flagella move liquid past the surface of the cell.
  •For single cells, such as sperm, this enables them to swim.
  •For cells anchored in a tissue, like the epithelial cells lining our air passages, this moves liquid over the surface of the cell (e.g., driving particle-laden mucus toward the throat).

Structure - Both cilia and flagella consist of:

•A cylindrical array of 9 filaments consisting of:
a complete microtubule extending into the tip of the cilium; a partial microtubule that doesn’t extend as far into the tip.
cross-bridges of the motor protein dynein that extend from the complete microtubule of one filament to the partial microtubule of the adjacent filament.
•a pair of single microtubules running up through the centre of the bundle, producing the “9+2” arrangement.
•The entire assembly is sheathed in a membrane that is an extension of the plasma membrane.

Motion of cilia and flagella is created by the microtubules sliding past one another. This requires:

• Motor molecules of dynein, which link adjacent microtubules together
• energy of ATP
• Dynein powers the sliding of the microtubules against one another — first on one side, then on the other.
• In organisms with flagella and cilia, the position of these is determined by the location of the centriole which becomes the basal body. They are made up with projections of microtubules from the cell body.
• Cilia and flagella move because of the axoneme and the arms attached to the microtubules, these arms are called axonemal dynein. ATP-dependent interactions of the dyneins with the neighbouring microtubule allow the movement of cilia and flagellum.