Note: This research was published as: Ghochani et al. , Biophys. J. 99, 3244 (2010).
Authors: Arlette Baljon1, Mariam Ghochani1, Terrence Frey2, Peter Salamon3, Jim Nulton3, John Waynelovich3 & Avinoam Rabinovitch4
1Department of Physics, 2Department of Biology, 3Department of Mathematics, San Diego State University, San Diego, CA (USA), 4Department of Physics, Ben-Gurion University of the Negev, Beer-Sheva (Israel).
Electron tomograms have revealed that in normal mitochondria the crista membrane self-assembles into a complex structure that contains both tubular and flat lamellar components. This structure is believed to be essential to the proper functioning of mitochondria as the powerhouse of the cell. It was indeed observed that the normal morphology is lost during programmed cell death - the mitochondrial inner membrane transforms into multiple vesicular matrix compartments.
We have constructed a model of the observed morphology. We show that it can be a minimum free energy configuration when we include in the total energy a term due to mechanical tensile forces acting along the direction of the tubules. Such forces could be exerted by proteins. Geometrical dimensions measured in 3D electron tomograms are inserted in the model to obtain thermodynamic quantities and the strength of tensile forces. Results for mitochondria in HeLa cells and mouse embryonic fibroblast show excellent agreement. The free-energy model predicts that the crista membrane structure of healthy mitochondria is stabilized by tensile forces of the order of 10 pN, comparable to those typical of motor proteins. The model also predicts reasonable values for the pressure difference across the crista membrane and its surface tension.
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