Biomedical Engineering Reference
In-Depth Information
prove.invaluable.in.tackling.design.obstacles.such.as.replicating.molecular.self-assembly.
pathways..Another.application.from.chemical.motors.is.the.ability.to.use.external.stimuli.
such.as.light.activation.as.a.power.source.(Balzani.et.al.,.2006)..Such.triggers.are.certain.to.
ind.useful.applications.when.incorporated.into.nanorobotic.designs.
In. modeling. propulsion. in. a. chemical. system,. simulations. along. with. experimental.
observations.are.useful..An.example.in.Shi.et.al..(2009).uses.energy.from.an.exothermic.fuel.
reaction.to.propel.a.structure.composed.of.an.open.rectangle.of.inert.atoms.that.has.walls.
peppered.with.catalytic.atoms..In.this.system,.energy.from.the.fuel.reaction.propels.the.
structure.upward.with.a.remarkable.velocity.analogous.to.rocket.propulsion..Newtonian.
momentum.transfer.describes.the.motion.resulting.from.this.asymmetric.catalysis..In.this.
type.of.simplistic.device,.critical.factors.include.temperature.and.the.permissibility.of.an.
inertial.body.moving.through.the.medium.in.which.the.chemical.motor.is.operating..In.this.
example,.the.gaseous.environment.of.fuel.atoms.is.very.different.from.the.more.viscous.
surroundings. characteristic. of. cellular. molecular. motors.. The. development. of. chemical.
motor.mechanisms.remains.rather.primitive.in.terms.of.eficacy,.control,.and.applications;.
nonetheless,.it.is.expected.to.provide.important.contributions.to.nanorobotics.
4.3 Cellular Cytoskeleton
4.3.1 A restless Architecture
The. cytoskeleton. in. eukaryotic. cells. is. an. elaborate. dynamic. structural. framework. that.
contributes.to.numerous.cell.processes.including.cell.shape.and.polarity,.cargo.transport,.
motility.and.turning,.cell.signaling,.chromosome.segregation,.and.cytokinesis..Multiple.
ilament.types.are.present.that.relect.different.functional.needs.and.employ.a.range.of.
associated.proteins.that.may.be.force-generating.motors,.nonmotile-associated.proteins,.
modiiers,. adaptors. or. regulators. allowing. for. dynamics,. and. structural. and. functional.
adaptability..The.complex.architectures.formed.respond.rapidly.to.external.stimuli.and.
to.a.multitude.of.intracellular.control.pathways.(Figure.4.2)..Universal.in.eukaryotes.are.
microtubules.and.actin.ilaments..Cellular.roles.for.actin.ilaments.were.once.thought.to.
(a)
(b)
(c)
Figure 4.2
(See companion CD for color igure.)
.The.microtubule.cytoskeleton.in.vivo..Human.ibroblast.cells.ixed.in.
glutaraldehyde.and.stained.for.α-tubulin.and.hoechst.(chromosomes)..The.replication.cycle.of.a.cell.includes.
temporal.changes.from.a.multifunctional.microtubule.array.to.the.highly.speciic.spindle.apparatus.required.for.
chromosome.segregation.into.newly.forming.daughter.cells..(a).Interphase.microtubule.arrays..(b).Metaphase.
spindle..(c).Mitotic.exit.and.cytokinesis..The.midbody.is.a.spindle.remnant.of.bundled.microtubules..Scale.bars.
are.(a).50.μm,.(b.and.c).10.μm..(Images.courtesy.of.Martin.Tomov,.CNSE,.University.at.Albany,.Albany,.NY.)
