When the green alga Chlamydomonas reinhardtii swims, it uses the breaststroke beat of its two flagella to pull itself forward . The flagellar waveform can be decomposed into a static component, corresponding to an asymmetric time-averaged shape, and a dynamic component, corresponding to the time-varying wave . Extreme lightening conditions photoshock the cell, converting the breaststroke beat into a symmetric sperm-like beat, which causes a reversal of the direction of swimming . Waveform conversion is achieved by a reduction in magnitude of the static component, whereas the dynamic component remains unchanged . The coupling between static and dynamic components, however, is poorly understood, and it is not known whether the static component requires the dynamic component or whether it can exist independently. We used isolated and reactivated axonemes  to investigate the relation between the two beat components. We discovered that, when reactivated in the presence of low ATP concentrations, axonemes displayed the static beat component in absence of the dynamic component. Furthermore, we found that the amplitudes of the two components depend on ATP in qualitatively different ways. These results show that the decomposition into static and dynamic components is not just a mathematical concept but that the two components can independently control different aspects of cell motility: the static component controls swimming direction, whereas the dynamic component provides propulsion.
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