NANOTECHNOLOGY—TECHNOLOGY ON A MOLECULAR SCALE - Chemistry: Notable Research and Discoveries - page 46

Strands of DNA self-assemble if they are complementary. For example,
a strand with the sequence AAGCT is complementary to TTCGA, and
will readily join via hydrogen bonds if mixed together in the same solu-
tion. The researchers create nanoparticles by attaching the components
to complementary strands of DNA. By customizing the sequences and
the positions of the attachments, Maye, Gang, and their coworkers can
maneuver the components in a variety of ways to form clusters or ag-
gregates. Some of this research has been published in a 2006 paper, “A
Simple Method for Kinetic Control of DNA-Induced Nanoparticle As-
sembly,” in the Journal of the American Chemical Society.
Nanoparticles can be employed in transportation, as mentioned for
Zubarev's assembly, as well as becoming components for larger assem-
blies. Some of these molecular assemblies can even function as minia-
ture motors.
MolECulArMACHInES
Examples of naturally occurring molecular machines and motors are al-
ready known. Proteins are the workhorses of cellular biology, perform-
ing functions such as transportation, communication, and structural
maintenance. Some of these proteins have moving parts and act exactly
like small machines.
Two examples are dynein and kinesin. These huge proteins latch
onto vesicles—membrane-bound compartments—filled with certain
molecules and transport this cargo to another region of the cell. The
proteins “walk” along filaments inside the cell, using the energy-rich
compound adenosine triphosphate (ATP) as fuel.
Another example is the enzyme that winds apart the two strands
of DNA. The hydrogen bonds hold the two strands of the double helix
together. Cellular mechanisms need to break apart those strands on oc-
casion to read a gene or to replicate its DNA, and they use enzymes to
perform this operation. The enzyme that speeds up the unwinding of
the strands is known as helicase. Helicase binds to DNA, and under
certain conditions the binding alone might provide enough leverage to
break the bonds. But Daniel S. Johnson, Michelle Wang, and their col-
leagues at Cornell University in Ithaca, New York, discovered that heli-
case does a little more—not only does it bind, it also yanks the strands
apart by exerting force. Wang and her research team made this finding