Essential Cell Biology 5th edition

460 CHAPTER 14 Energy Generation in Mitochondria and Chloroplasts
CARDIAC MUSCLE
mitochondria
SPERM TAIL
(C)
mitochondria
flagellar core
(A) (B) (D)
myofibril of
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contractile apparatus
Figure 14–6 Mitochondria are located near sites of high ATP utilization. (A) In a cardiac muscle cell, mitochondria
are located close to the contractile apparatus, where ATP hydrolysis provides the energy for contraction. The
structure of the contractile apparatus is discussed in Chapter 17. (B) An electron micrograph of cardiac muscle shows
a preponderance of mitochondria. (C) In a sperm, mitochondria are located in the tail, wrapped around a portion of
the motile flagellum that requires ATP for its movement. The internal structure of the flagellar core is discussed in
Chapter 17. (D) Micrograph showing
ECB5 n14.100-14.06
a flagellum that has been thinly sliced to reveal the internal core structure as
well as the surrounding mitochondria. (B, Keith Porter papers, Center for Biological Sciences Archives, University of
Maryland, Baltimore Country; D, from W. Bloom and D.W. Fawcett, A Textbook of Histology, 10th ed. Philadelphia:
W.B. Saunders Company, 1975. Reprinted with permission from the Estate of D.W. Fawcett.)
Mitochondria are present in large numbers—1000 to 2000 in a liver cell,
for example. But their numbers vary depending on the cell type and can
change with the energy needs of the cell. In skeletal muscle cells that
have been repeatedly stimulated to contract, mitochondria can divide
until their numbers increase five- to tenfold. Marathon runners, for example,
may have twice the volume of mitochondria in their leg muscles than
do individuals who are more sedentary.
Regardless of their varied appearance, location, and number, however,
all mitochondria have the same basic internal structure—a design that
supports the efficient production of ATP, as we see next.
A Mitochondrion Contains an Outer Membrane, an
Inner Membrane, and Two Internal Compartments
An individual mitochondrion is bounded by two highly specialized
membranes—one inside the other. These membranes, called the
inner and outer mitochondrial membranes, create two mitochondrial
mitochondria
nucleus
continuous mitochondrion
Figure 14–7 Mitochondria often form
elongated, tubular networks, which can
extend throughout the cytoplasm.
(A) Mitochondria (red ) are fluorescently
labeled in this cultured mouse fibroblast.
(B) In a yeast cell, the mitochondria (red )
form a continuous network, tucked
against the plasma membrane. (A, courtesy
of Carl Zeiss Microscopy, LLC; B, from
J. Nunnari et al., Mol. Biol. Cell 8:1233–1242,
1997. With permission from The American
Society for Cell Biology.)
(A)
(B)
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