The State of Biophysics - Biophysical Journal

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perform life’s central functions. Yet these molecules by
themselves are not alive, and they function only when they
work in the cellular milieu. How living cells come alive
through the concerted actions of individual molecules is a
major challenge for future research. Researchers are making
progress on multiple fronts.
On one front we might call ‘‘extreme in vitro,’’ we can
measure multiple properties from single-molecular assem-
blies. FRET can be extended up to four colors, allowing
us to measure six distances simultaneously. This can also
be combined with multiaxis optical tweezers to study, for
example, DNA replication, which is an amazingly rapid
and accurate process that requires more than a dozen
different proteins, with single basepair resolution, while at
the same time probing how many proteins of which kind
are present at each step of the reaction. On another front,
we can push the technology to the cellular level, and even
to the tissue level, ultimately hoping to view single-mole-
cule activities in living cells in full glorious detail. Finally,
we might find a third way, where protein complexes can
be captured from freshly sacrificed cells or animals, or pa-
tient tissues, for detailed single-molecule analysis.
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Biophysical Journal 110(5) 1004–1007
Probing Nature’s Nanomachines 1007