Biology 12

Chapter 3 Cellular Energy • MHR 69

3.2 Moving to the Mitochondrion

into the interior of the mitochondrion to be broken

down further. The inner membrane contains a high

proportion of cardiolipin, a phospholipid that

makes this membrane especially impermeable to

ions. This relative impermeability, as you will

discover when you learn about chemiosmosis, is

very important in the production of ATP.

The intermembrane space is a fluid-filled area

containing enzymes that use ATP. During the

synthesis of ATP, the intermembrane space serves

as a hydrogen ion (H+) reservoir, storing the

hydrogen ions that will be used for ATP synthesis.

Finally, the inner mitochondrial compartment,

comprised of the matrix and the cristae, remains

relatively isolated from the outer mitochondrial

membranes. The inner membrane contains the

multienzyme complexes and the electron carriers

of the electron transport chain. During aerobic

cellular respiration, the transfer of electrons

through this chain creates a high hydrogen ion (H+)

EXPECTATIONS

Describe the energy transformations that occur in aerobic cellular respiration.

Explain the role of enzymes in metabolic reactions in the mitochondrion.

Interpret qualitative data in a laboratory investigation of enzyme activity in

the Krebs cycle.

Explain the process of anerobic cellular metabolism.

Research and describe how cellular processes are used in the food industry.

cristae

outer

membrane

intermembrane space inner membrane

matrix

200 nm

Figure 3.7Structure of the mitochondrion

Whereas glycolysis occurs in the cell cytosol, the
remaining reactions of aerobic cellular respiration
take place inside the mitochondria. As you have
learned in previous studies, mitochondria are
small organelles found in eukaryotic cells. A
mitochondrion is composed of an outer and inner
membrane, separated by an intermembrane space,
as shown in Figure 3.7. The inner membrane folds
as shelf-like cristae and contains the matrix, an
enzyme-rich fluid. The cristae and the matrix
are the sites where ATP synthesis occurs. More
mitochondria are found in cells that require
more energy, such as muscle and liver cells.
The two mitochondrial membranes have
important differences in their biochemical
composition. The outer membrane contains a
transport protein called porinthat makes it
permeable to all molecules of 10 000 u (atomic
mass units) or less. It also contains enzymes that
help convert fatty acids to molecules that can pass