Flagellar Oars Beat Like Galley Slaves In Synchronization
The Dec. 14 issue of Current Biology1 investigated another mystery in the operation of eukaryotic flagella:
Flagella are microtubule-based structures that propel cells through the surrounding fluid. The internal structure of a flagellum consists of nine parallel doublet microtubules arranged around a central pair of singlet microtubules (Figure 1). Force for propulsion is provided by thousands of dynein motors anchored in rows along one side of each doublet, which can walk along the microtubule of the adjacent doublet. In order to produce coordinated bending of the flagellum, these dynein motors — organized into multi-headed complexes called the inner and outer dynein arms — must produce their power strokes in synchrony, like the oarsmen on an ancient Mediterranean war-galley. But whereas oar-strokes were coordinated by a continuous drum-beat, it is much less clear how flagellar dynein motors are synchronized.
The authors of the paper consider growing evidence that the central microtubule pair provides the drumbeat, with the aid of “a protein complex called the dynein regulatory complex, located between the spokes and the dynein arms.” However, “The molecular mechanism by which the central pair regulates dynein is not known.”
1Kimberly A. Wemmer and Wallace F. Marshall, “Flagellar Motility: All Pull Together,” Current Biology Volume 14, Issue 23, 14 December 2004, Pages R992-R993, doi:10.1016/j.cub.2004.11.019.
Thus another deeper level of complexity becomes apparent. A collection of parts is not enough; they must coordinate their actions. No wonder Antony Flew considered Darwin’s Black Box an “amazing book” and has become a theist (see 12/09/2004 entry).