Essential Cell Biology 5th edition

18 CHAPTER 1 Cells: The Fundamental Units of Life
outer membrane
inner membrane
(B)
(C)
(A)
Figure 1–18 Mitochondria have a
distinctive internal structure. (A) An
electron micrograph of a cross section
of a mitochondrion reveals the extensive
infolding of the inner membrane.
(B) This three-dimensional representation
of the arrangement of the mitochondrial
membranes shows the smooth outer
membrane (gray) and the highly convoluted
inner membrane (red ). The inner membrane
contains most of the proteins responsible
for energy production in eukaryotic cells; it
is highly folded to provide a large surface
area for this activity. (C) In this schematic
cell, the innermost compartment of the
mitochondrion is colored orange.
(A, courtesy of Daniel S. Friend, by
permission of E.L. Bearer.)
100 nm
cells (Figure 1–19). This evidently created a symbiotic relationship in
which the host eukaryote and the engulfed bacterium helped each other
to survive and reproduce.
Chloroplasts Capture Energy from Sunlight
ECB5 e1.17/1.18
Chloroplasts are large, green organelles that are found in the cells of
plants and algae, but not in the cells of animals or fungi. These organelles
have an even more complex structure than mitochondria: in addition to
their two surrounding membranes, they possess internal stacks of membranes
containing the green pigment chlorophyll (Figure 1–20).
early anaerobic
eukaryotic cell
nucleus
internal
membranes
early aerobic
eukaryotic cell
Figure 1–19 Mitochondria are thought to
have evolved from engulfed bacteria. It is
virtually certain that mitochondria evolved
from aerobic bacteria that were engulfed
by an archaea-derived, early anaerobic
eukaryotic cell and survived inside it, living
in symbiosis with their host. As shown in this
model, the double membrane of presentday
mitochondria is thought to have been
derived from the plasma membrane and
outer membrane of the engulfed bacterium;
the membrane derived from the plasma
membrane of the engulfing ancestral cell
was ultimately lost.
bacterial outer membrane
aerobic bacterium
bacterial plasma
membrane
loss of membrane
derived from early
eukaryotic cell
mitochondria with
double membrane