Tensile Forces and Shape Entropy Explain Observed Crista Structure in Mitochondria

TL;DR

This study presents a model explaining mitochondrial inner membrane morphology as a balance of bending, tension, and entropy, supported by 3D electron tomography measurements of mitochondrial structures in cells.

Contribution

The paper introduces a novel free energy model incorporating tension and entropy to explain mitochondrial cristae structure, validated by experimental tomography data.

Findings

Tensile forces of about 10 pN stabilize cristae phases.

The model predicts a pressure difference of approximately -0.036 atm.

Structural features of mitochondria support the role of tension and entropy in membrane morphology.

Abstract

A model is presented from which the observed morphology of the inner mitochondrial membrane can be inferred as minimizing the system's free energy. Besides the usual energetic terms for bending, surface area, and pressure difference, our free energy includes terms for tension that we believe to be exerted by proteins and for an entropic contribution due to many dimensions worth of shapes available at a given energy. In order to test the model, we measured the structural features of mitochondria in HeLa cells and mouse embryonic fibroblasts using 3D electron tomography. Such tomograms reveal that the inner membrane self-assembles into a complex structure that contains both tubular and flat lamellar crista components. This structure, which contains one matrix compartment, is believed to be essential to the proper functioning of mitochondria as the powerhouse of the cell. We find that tensile forces of the order of 10 pN are required to stabilize a stress-induced coexistence of tubular and flat lamellar cristae phases. The model also predicts \Deltap = -0.036 \pm 0.004 atm and \sigma=0.09 \pm 0.04 pN/nm.