The application of physical techniques to the study of life has long been hindered by the sheer complexity of such systems, but over the past few decades, the ability to probe the biological world has greatly improved.
Biophysics in its Infancy
In 1914, Max von Laue won the Nobel Prize in physics for discovering that X-rays are diffracted by crystals, and that they could be used to determine structural properties of certain crystalline materials. It took almost 40 years for Watson and Crick (along with significant help from Maurice Wilkins and Rosalind Franklin) to use the same technique to unravel the structure of DNA.
Another early attempt to use the techniques of physics to investigate a biological system was also made by Crick in 1949. He inserted extremely small magnetic particles into a living cell, applied an external force with the use of an electromagnet, and observed their motion. The tiny magnets crept through the cell’s cytoplasm, but due to the then poor understanding of a cell’s internal structure, few solid conclusions could be made, and follow-up experiments were never made.
Modern Biological Physics
Decades later, such ideas have stormed back into the research labs, with magnets, lasers, and microscopic needles all being used to prod and poke at a huge range of biological samples.
The Atomic Force Microscope (AFM), for example, uses an ultra-sharp tip to "feel" the surface of a cell, or to stretch a biological molecule, such as DNA. The minute deflections of the tip as it glides across a surface are measured by reflections of a laser beam from the back of the probe.
Another imaging technique, known as electron microscopy, uses beams of electrons to view samples at magnifications far greater than standard light microscopy.
For manipulation, laser tweezers use a tightly focussed laser beam to exert a force upon a microscale (millionth of a meter) or nanoscale (billionth of a meter) particle, allowing incredibly small forces to be applied to a sample. One application is the use of laser tweezers to measure the mechanical properties of structures such as cell walls.
Crick’s original idea to use magnetic particles has also advanced, thanks to the integration of computer hardware and improved optics to accurately track the particle’s position and motion. The mechanical properties of DNA have been extensively studied using such an instrument, as have the structural differences between samples of blood clots.
In conjunction with the use of modern instruments, physical models have also advanced, again thanks to increases in computer speed and ability. Biological systems can be virtually tested using computer models (based upon thermodynamics and statistical mechanics) and the results compared with experimental data. This adds a mathematical rigour to the studies, and further extends the overall understanding of these complicated systems.
The Future of Biophysics
As instrumentation becomes increasingly sophisticated, the understanding of the biological world is likely to expand to encompass ever larger systems. Today, single molecules are being investigated and modelled. This will eventually advance to groups of molecules, groups of cells, and perhaps even entire organisms.
References:
Nolting, Bengt. Methods in Modern Biophysics. Springer; 2nd ed. edition (September 6, 2005)
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