Unformatted text preview: s like this are coiled bundles of filam ents that expand or contract in res pons e to chem ical cues . A wave of
pos itively charged calcium ions , for exam ple, neutralizes the negative charges that keep the filam ents extended.
Som e s perm us e s pringlike engines m ade of actin filam ents to s hoot out a barb that penetrates the layers that
s urround an egg. And certain virus es us e a s im ilar apparatus to s hoot their DNA into the hos tâ€™s cell.
Ratchets are als o us eful for m oving whole cells , including s om e other s perm s and pathogens . Thes e engines
are filam ents that s im ply grow at one end, attracting chem ical building blocks from nearby. Becaus e the other
end is anchored in place, the growing end pus hes agains t any barrier that gets in its way.
Both s prings and ratchets are m ade up of s m all units that each m ove jus t s lightly, but collectively produce a
powerful m ovem ent. Ultim ately, Mahadevan and Mats udaira hope to better unders tand jus t how thes e particles
create an effect that s eem s to be s o m uch m ore than the s um of its parts . Migh...
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This document was uploaded on 03/23/2014.
- Summer '14