Biomedical Engineering Reference
In-Depth Information
100
100
Overstretching
transition
dsDNA
80
80
Overstretching
plateau
60
60
ssDNA
Intrinsic
elasticity
40
40
20
20
Entropic
elasticity
0
0
1
2
3 4
Extension (μm)
5
6
0.2
0.4
DNA extension (nm/bp)
0.6
(a)
(b)
180
160
140
120
8 nm
20 nm
100
80
60
2
3 4
Time (s)
5
6
7
1
3
5
7
0
1
(c)
(d)
Time (s)
Figure 19.7
Applications. of. optical. tweezers. in. biomechanics.. (a). The. force-extension. dynamics. for. a. single. B-type. DNA.
molecule.. (Hormeno,. S.. and. Ricardo. Arias-Gonzalez,. J.:. Exploring. mechanochemical. processes. in. the. cell. with.
optical.tweezers..
Biol. Cell
..2006..98..679-695..Copyright.Wiley-VCH.Verlag.GmbH.&.Co..KGaA..Reproduced.with.
permission.).(b).The.measured.force-extension.curve.of.a.dsDNA.(hollow.triangles).and.ssDNA.(right.black.line).
molecule.and.the.theoretical.curve.(the.left.black.line).showed.the.overstretching.transition.from.dsDNA.to.ssDNA..
(Reproduced.with.permission.from.Williams,.M.C.,.Rouzina,.I.,.and.Bloomield,.V.A.,.Thermodynamics.of.DNA.
interactions.from.single.molecule.stretching.experiments,.
Acc. Chem. Res
.,.35,.159-166,.Copyright.2002,.American.
Chemical. Society.). (c). The. unfolding. of. the. multidomain. protein. titin.. A. titin. molecule. is. pulled. and. held. for. a.
certain.end-to-end.length.and.the.holding.force.varies.due.to.unfolding-induced.molecular.expansion..(Reprinted.
by. permission. from. Macmillan. Publishers. Ltd..
Nature
,. Tskhovrebova,. L.,. Trinick,. J.,. Sleep,. J.A.,. and. Simmons,.
R.M.,.Elasticity.and.unfolding.of.single.molecules.of.the.giant.muscle.protein.titin,.387,.308-312,.Copyright.1997.).
(d).The.tracking.curve.of.the.movement.of.a.single.kinesin.along.a.microtubule.with.an.average.discrete.step.of.
8.nm..(Reprinted.by.permission.from.Macmillan.Publishers.Ltd..
Nature
,.Schnitzer,.M.J..and.Block,.S.M.,.Kinesin.
hydrolyses.one.ATP.per.8-nm.step,.388,.386-390,.Copyright.1997.)
force.magnitude.in.each.stage.could.vary.with.their.molecular.structures.and.the.actual.
physiological.conditions.(e.g.,.pH.value,.ionic.strength,.or.temperature)..Similar.strategies.
are. also. used. in. the. mechanics. study. of. ssDNA,. RNA,. or. hybrid. DNA-RNA. linkers..
Compared. to. dsDNA,. these. polynucleic. acid. chains. are. generally. more. lexible. and. the.
force. required. for. deformation. is. also. much. less.. In. Figure. 19.7b,. the. theoretical. curves.
for.both.dsDA.and.ssDNA.are.shown..The.difference.between.the.measured.dynamics.of.
dsDNA.and.these.two.curves.is.from.the.overstretched.transition.from.the.dsDNA.to.the.
ssDNA.form.of.its.molecular.chain..Besides.force.measurement,.the.two.complementary.
strands.of.dsDNA.molecules.may.also.be.progressively.separated.or.unzipped.by.pulling.
and.twisting.tethered.DNA.ends..The.torque-induced.deformation.also.helps.reveal.the.
