Biophysicists apply tools and concepts from physics to the understanding of living systems at the molecular level. This field promises to yield answers to important questions about the structure, dynamics, function, and interactions of biological molecules such as proteins and nucleic acids. New instruments are allowing researchers to measure distances much shorter than the wavelength of light (nanometers) and forces as small as one trillionth of the force required to hold an apple against Earth's gravity (piconewtons). At JILA, biophysics researchers study protein dynamics, single molecule biophysics, and RNA folding dynamics. They are looking for answers to the following questions:

• How does enzyme flexibility change in response to light, binding-partner interactions, co-factor substitution, or voltage changes?
• What kinds of new measurements will enable the "squishiness" of human cells to be related to cell type and health?
• Is it possible to image a single protein attached to the surface of a cell?
• How do we combine advanced laser spectroscopy techniques with microfluidics devices into a "molecular evolution machine" to develop new fluorescent proteins and sensors for biological imaging?
• What are the kinetics of binding and folding for single RNA molecules?
• What is the role of cations in RNA folding?
• What is the most precise way to measure and apply forces to individual biomolecules?

To answer these questions, JILA researchers use precision tools such as optical tweezers, lasers, laser microscopy, atomic force microscopy, and high-resolution spectroscopy. Optical tweezers are a focused laser beam that can manipulate micron-sized beads in solution. Lasers emit bursts of photons in pulses ranging from femto- to nanoseconds (10^-15–10^-9 seconds), allowing scientists to take "photographs" of rapidly vibrating biomolecules under a variety of experimental conditions. These photographs allow the scientists to observe how proteins and nucleic acids move, twist, fold, and interact. Laser microscopes incorporating microfluidics technology permit the study of protein motions on varying time scales in the same system. One type of high resolution spectroscopy, known as fluorescence resonance energy transfer (FRET) spectroscopy, employs laser-scanning microscopes to observe the motions of proteins or RNA pretreated to change color when they absorb light.