1. Pyruvate and fatty acids donate acetyl groups to the citric acid cycle. This
generates electron carriers such as NADH.
2. NADH donates a pair of high-energy electrons to the electron transport
3. As electrons move along the electron transport chain (also known as the
respiratory chain), some of their energy is lost at discrete steps. The
energy is captured by the components of the chain, which use it to pump
H+ ions out of the matrix. This establishes an H+ gradient across the
4. The H+ gradient is utilized by the ATP synthase. H+ ions flow down their
gradient through the synthase. This is an energy releasing process. Some
of the energy is captured by the synthase, which uses it to make ATP.
NADH Transfers its Electrons to Oxygen Through Three Large Respiratory
!As mentioned, some components of the electron transport chain can harness the
energy from electrons and pump H+ out of the matrix. In eukaryotes, these are typically
three large proteins complexes. We will consider how they work later in this chapter.
As Electrons Move Along the Respiratory Chain, Energy Is Stored as an
Electrochemical Proton Gradient Across the Inner Membrane
!We already discussed this with regard to Figure 14-10.
The Proton Gradient Drives ATP Synthesis
!Ion gradients contain energy. When ions flow down a gradient, this is an energy
releasing process. As we discussed in Chapter 11, an electrochemical gradient has a
chemical and an electrical component. This idea is shown in Figure 14-13.
!A portion of Figure 14-10 is magnified and shown in Figure 14-14. The H+
gradient that is generated by the electron transport chain is utilized by the ATP synthase.
The way the ATP synthase utilizes the gradient is pretty amazing (Figure 14-15). H+ ions
flow through the membrane portion of the protein. This causes a rotor (gamma subunit)
to spin. Note: the gamma subunit is not labeled in Figure 14-15. It’s the red thing that is
poking into the green complex of alpha and beta subunits. As the gamma subunit spins, it
causes the beta subunits to undergo a series of changes in their conformational states:
1. The beta subunits begin with a conformation that has a
relatively low affinity for ADP and phosphate.
2. As the gamma subunit spins, it causes the beta subunits to
switch to a conformation with a very high affinity for these
substrates. This tight binding facilitates the formation of a
covalent bond to create ATP, which initially has a high
affinity for the beta subunit.
3. Another conformational change causes the beta subunit to
have a low affinity for ATP. Therefore, ATP is released, and
the processes can start all over again.
The Proton Gradient Drives Coupled Transport Across the Inner Membrane
!We have already discussed symport and antiport in Chapter 11. You should be
familiar with the transporters shown in Figure 14-16. Symporters are used for the uptake
of pyruvate and phosphate into the matrix. An antiporter is used to take up ADP and