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Undulipodium

A eukaryotic flagellum is sometimes called a cilium or undulipodium, and it is completely different from prokaryotic flagella in its structure and evolutionary origin in the cell. Since the flagella of prokaryotes and eukaryotes have nothing in common except basic location and function, and since flagella usually refers to the prokaryotic version, it's common to call the eukaryotic flagellum an undulipodium.

The undulipodium is composed of nine fused pairs of microtubules that surround a core of two central unfused microtubules; this structure is called an axoneme. Where the undulipodium attaches to the cell is a basal body, or kinetosome, which directs the movement of the undulipodium. The entire undulipodium is encased in the cell's plasma membrane and accessible to cytoplasm. Each of the nine fused pairs extends two dynein arms to the adjacent microtubule, and the force applied by the arms causes the undulipodium to bend, providing movement. The energy for this motion is provided by ATP synthesis from the kinetosome.

The undulipodium is not just involved in motion, but also in sensation and signal transduction. It is classified as an organelle.

Web Resources On Undulipodium

Cellular Ultrastructure
Flagellated Protozoa

Book Resources On Undulipodium

Organelles, Genomes and Eukaryote Phylogeny: An Evolutionary Synthesis in the Age of Genomics by Robert P. Hirt
Molecular biology: A comprehensive introduction to prokaryotes and eukaryotes by David Freifelder

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