Botany · Ch 6 — Cell: The Unit of Life
Eukaryotic Flagellum
Eukaryotic Flagellum
A eukaryotic flagellum is a considerably more elaborate structure than its bacterial counterpart, and it is powered completely differently. It is enclosed within an extension of the cell's own plasma (unit) membrane, and it arises from a basal body sitting just below the cell surface; moving outward from that base, its structure includes the basal body itself, supporting rootlets, a basal plate, and finally the long projecting shaft, called the axoneme. The axoneme is built from microtubules made of the protein tubulin, arranged in the classic '9+2' pattern: nine paired (doublet) microtubules arranged in a circle around the periphery, surrounding a further pair of two single, central microtubules. A eukaryotic flagellum is considerably longer than a cilium - it can reach up to about 200 micrometres in length. The actual bending movement of the flagellum is generated by the motor protein dynein, which projects from the outer microtubule doublets and connects them both to each other and in to the central pair of microtubules; separately, a second linking protein, nexin, holds the peripheral doublets together with each other. Movement itself is powered directly by ATP: dynein uses the chemical energy released f …
What this figure shows. A cross-section through the axoneme showing the classic 9+2 arrangement: nine outer doublets of microtubules arranged in a circle around two single central microtubules, with dynein arms projecting from each outer doublet toward its neighbour and toward the central pair, and nexin links connecting adjacent outer doublets to each other; the whole axoneme is shown enclosed within an extension of the plasma membrane and rooted at …