Molecular Biology of the Cell by Bruce Alberts, Alexander Johnson, Julian Lewis, David Morgan, Martin Raff, Keith Roberts, Peter Walter by by Bruce Alberts, Alexander Johnson, Julian Lewis, David Morg

THE MITOCHONDRION
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Figure 14–7 Interaction of mitochondria with the endoplasmic reticulum.
(A) Fluorescence light microscopy shows that tubules of the ER (green) wrap
around parts of the mitochondrial network (red) in mammalian cells. The
mitochondria then divide at the contact sites. After contact is established,
fission occurs within less than a minute, as indicated by time-lapse
microscopy. (B) Schematic drawing of an ER tubule wrapped around part of
the mitochondrial reticulum. It is thought that ER–mitochondrial contacts also
mediate the exchange of lipids between the two membrane systems.
(A, adapted from J.R. Friedman et al., Science 334:358–362, 2011.)
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The Mitochondrion Has an Outer Membrane and an Inner
Membrane
Like the bacteria from which they originated, mitochondria have an outer and
an inner membrane. The two membranes have distinct functions and properties,
and delineate separate compartments within the organelle. The inner membrane,
which surrounds the internal mitochondrial matrix compartment (Figure 14–8),
is highly folded to form invaginations known as cristae (the singular is crista),
which contain in their membranes the proteins of the electron-transport chain.
Where the inner membrane runs parallel to the outer membrane, between the
cristae, it is known as the inner boundary membrane. The narrow (20–30 nm) gap
between the inner boundary membrane and the outer membrane is known as
the intermembrane space. The cristae are about 20 nm-wide membrane discs
or tubules that protrude deeply into the matrix and enclose the crista space. The
crista membrane is continuous with the inner boundary membrane, and where
their membranes join, the membrane forms narrow membrane tubes or slits,
known as crista junctions.
Like the bacterial outer membrane, the outer mitochondrial membrane is
freely permeable to ions and to small molecules as large as 5000 daltons. This
(A)
mitochondrion
(B)
ER tubule
1 µm
outer
membrane
crista space
intermembrane outer membrane
space
inner boundary
MBoC6 n14.431/14.07 membrane
cristae
intermembrane
space
matrix
inner boundary
membrane
cristae
crista junction
crista
membrane
(C)
crista space
crista junction
(B)
matrix
(A)
200 nm
Figure 14–8 Structure of a mitochondrion. (A) Tomographic slice through a three-dimensional map of a mouse heart mitochondrion determined by
electron-microscope tomography. The outer membrane envelops the inner boundary membrane. The inner membrane is highly folded into tubular
or lamellar cristae, which crisscross the matrix. The dense matrix, which contains most of the mitochondrial protein, appears dark in the electron
microscope, whereas the intermembrane space and the crista space appear light due to 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 cristae junctions, where the cristae join the
inner boundary membrane. (B) Tomographic surface-rendered portion of a yeast mitochondrion, showing how flattened cristae project into the matrix
from the inner membrane (Movie 14.2). (C) Schematic drawing MBoC6 of a mitochondrion n14.305/14.08 showing the outer membrane (gray), and the inner membrane
(yellow). Note that the inner membrane is compartmentalized into the inner boundary membrane and the crista membrane. There are three distinct
spaces: the inner membrane space, the crista space, and the matrix. (A, courtesy of Tobias Brandt; B, from K. Davies et al., Proc. Natl Acad. Sci.
USA 109:13602–13607, 2012. With permission from the National Academy of Sciences.)