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 Rabinovitch^4
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.