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Unformatted text preview: earned to burn ATP and us e the energy to change s hape. â€œWeâ€™ll
never really know, becaus e we canâ€™t dig up the rem ains of ancient proteins , but that was probably a big
evolutionary leap,â€ays Vale.
On a s lightly larger s cale, loner cells like s perm or infectious bacteria are prim e m overs that res olutely pus h
their way through to other cells . As L. Mahadevan and Paul Mats udaira of the Mas s achus etts Ins titute of
Technology explain, the engines in this cas e are s prings or ratchets that are clus ters of m olecules , rather than
s ingle protein like m yos in and kines in. Res earchers donâ€™t yet fully unders tand thes e engines â€™ fueling
proces s or the details of how they m ove, but the res ult is a force to be reckoned with. For exam ple, one s uch
engine is a s pringlike s tall connecting a s ingle-celled organis m called a vorticellid to the leaf fragm ent it calls
hom e. When expos ed to calcium , the s pring contracts , yanking the vorticellid down at s peeds approaching 3
inches (8 centim eters ) per s econd. Spring...
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This document was uploaded on 03/23/2014.
- Summer '14