What Is Biophysics?

Biophysics is a discipline concerned with applying the principles and methods of physics to the study of biological systems. It uses mathematical analysis, physical measurement, and computational modeling to understand how living matter is organized and how it functions, from the folding of individual proteins to the electrical signaling of neurons to the mechanics of muscle contraction. The field occupies the intersection of biology, chemistry, physics, and engineering, and it seeks to describe life in terms of quantifiable physical laws.

The discipline emerged from nineteenth-century physiology and from early twentieth-century investigations into the electrical properties of nerve membranes and the X-ray diffraction structures of biological molecules. The 1953 determination of the DNA double helix by Watson, Crick, Franklin, and Wilkins is among the most celebrated contributions that biophysical methods made to biology. Since then, the Biophysical Society has identified the field as encompassing every scale of living matter, from atoms and molecules through cells, tissues, and whole organisms to ecosystems.

Molecular and Structural Biophysics

Molecular biophysics focuses on the physical properties of proteins, nucleic acids, lipids, and their complexes. Techniques such as X-ray crystallography, cryo-electron microscopy (cryo-EM), nuclear magnetic resonance (NMR) spectroscopy, and single-molecule force spectroscopy are used to determine atomic-resolution structures and to measure the forces that stabilize and drive molecular machines. Cryo-EM, in particular, has transformed the field since the mid-2010s by enabling near-atomic resolution imaging of large complexes that resist crystallization. These structural insights are essential for understanding enzyme catalysis, membrane transport, and the mechanisms by which pathogens evade the immune system.

Computational Biophysics

Computational biophysics uses computer simulations and mathematical models to study biological systems at scales and timescales that are difficult to access experimentally. Molecular dynamics (MD) simulation, for instance, integrates Newton's equations of motion over millions of time steps to track the movement of every atom in a protein-solvent system. Quantum mechanical calculations model electron transfer reactions in photosynthesis and enzymatic active sites. At larger scales, finite-element models describe the mechanical behavior of cells and tissues under applied forces. A 2016 perspective in PMC on the quantitative approach to biophysics notes that computational methods have become as central to biophysics as bench experiments, because they allow systematic exploration of parameter spaces too large for experimental sampling.

Biophysical Measurement Methods

The experimental toolkit of biophysics extends well beyond the structural methods used for molecular imaging. Patch-clamp electrophysiology measures ionic currents through individual ion channels in cell membranes with sub-picoampere precision, a capability that revealed the gating mechanisms of voltage-sensitive channels central to nerve conduction. Atomic force microscopy (AFM) images biological surfaces and measures piconewton-scale adhesion forces between receptor-ligand pairs. Fluorescence resonance energy transfer (FRET) reports nanometer-scale distances between molecular pairs, enabling real-time observation of conformational changes in living cells. Each of these methods requires careful attention to how the physical measurement perturbs the biological system being studied, a balance that distinguishes biophysical work from purely physical instrumentation.

Applications

Biophysics has applications in a range of fields, including:

• Drug discovery: structure-based drug design using protein crystal structures and MD simulations
• Medical imaging: the physical principles of MRI, PET, and ultrasound all derive from biophysics
• Biomedical engineering: mechanical modeling of bone, cartilage, and soft tissue for implant design
• Neuroscience: biophysical models of neural circuits underpinning brain-machine interface development
• Synthetic biology: rational design of molecular motors and gene regulatory networks