A physicist at the University of Arkansas has defended the validity of the
Stokes-Einstein equation, one of Albert Einstein’s most famous equations, as
it relates to biology. The research will help scientists better understand
antibiotic resistance and the mechanical properties of cancer cells.
Working with proteins in live bacteria, Yong Wang, assistant professor in
the Fulbright College of Arts and Sciences, tested the 117-year-old
equation, which provided evidence for the reality of atoms and molecules. He
found that the famous equation remained valid for explaining how molecules
move inside bacteria.
“Bacterial cytoplasm is not a simple soup,” Wang said. “Our study showed
that it might be more like spaghetti with tomato sauce and meatballs.”
Cytoplasm is the crowded and complex material inside bacteria. It has high
concentrations of large biological molecules, including millions of
proteins, carbohydrates and salts, and all kinds of polymers and filaments,
such as DNA and RNA.
Wang found that although Einstein’s equation appeared to be off for
proteins’ motion within live bacteria, it remained valid by taking into
account the entangled polymers and filaments inside bacteria.
The so-called Einstein relation - also called the Stokes-Einstein equation -
is one of Albert Einstein’s major research accomplishments in his “year of
miracles,” 1905. Explaining the mobility of particles through liquid, the
equation has been characterized as a stochastic model for Brownian motion,
meaning particles move around randomly because of collisions with
surrounding molecules. Most importantly, the theory provided early empirical
evidence for the reality of atoms and molecules.
However, over the past two decades, scientists have challenged the theory’s
validity as it applies to what’s inside live cells and bacteria. Wang’s
study adds to this body of knowledge, helping resolve the current
controversy.
More importantly, it provides a foundation for assessing the mechanical
properties of cells and bacteria based on the Einstein relation. This should
help scientists understand antibiotic resistance of certain microorganisms
and the mechanical properties of cancer cells, which differ from than the
mechanical properties of normal, healthy cells.
Reference:
Asmaa A. Sadoon, William F. Oliver, and Yong Wang, Revisiting the
Temperature Dependence of Protein Diffusion inside Bacteria: Validity of the
Stokes-Einstein Equation, Phys. Rev. Lett. 129, 018101, DOI: 10.1103/PhysRevLett.129.018101