Fig. 3

Tomographic volume of mouse heart mitochondrion. a Three-dimensional volume of a mouse heart mitochondrion determined by cryo-ET. The outer membrane (grey) envelops the inner membrane (light blue). The inner membrane is highly folded into lamellar cristae, which criss-cross the matrix. b Tomographic slice through the map volume. The dense matrix, which contains most of the mitochondrial protein, appears dark in the electron microscope, whereas the intermembrane space and crista lumen appear light because of their lower protein content. The inner boundary membrane follows the outer membrane closely at a distance of ~20 nm. The inner membrane turns sharply at the crista junctions, where the cristae join the inner boundary membrane. (Courtesy of Tobias Brandt)