BIOL 4004 Lecture Notes - Lecture 1: Electronic Component, Phosphatidylserine, Ionophore
6 pages44 viewsFall 2015
Course CodeBIOL 4004
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MBC5 Study Guide – Chapter 14
(Energy Conversion: Mitochondria and Chloroplasts)
!Two cellular organelles, the mitochondria, which are found in all eukaryotic
cells, and the chloroplasts, which are found in plant cells, play a key role in energy
conversion. The mitochondria break down food molecules and repackage most of the
energy in the form of ATP. Chloroplasts capture light energy and use it to synthesize
organic molecules. We will mostly concentrate on mitochondria. As shown in Figure 14-
1, both organelles can carry out chemiosmotic coupling. During this process, the energy
within an ion electrochemical gradient is used to drive the synthesis of ATP. This is an
energy interconversion because gradient energy is converted to chemical bond energy.
!In this section, we will primarily focus on the structure of mitochondria and their
ability to metabolize food molecules. We will also consider the general features of
chemiosmosis as it occurs in mitochondria.
The Mitochondrion Contains an Outer Membrane, an Inner Membrane, and Two
!As shown at the top of Figure 14-7, the mitochondrion has two membranes, an
outer and inner membrane. In the experiment shown in this figure, the two types of
membrane can be separated by osmotic swelling and differential centrifugation. In this
course, we will primarily focus our attention on the membrane proteins found in the inner
mitochondrial membrane, and on the events in the matrix.
The Citric Acid Cycle Generates High-Energy Electrons
!As you will recall from your Biochemistry course, the process called glycolysis
involves the breakdown of glucose into pyruvate. This occurs in the cytosol. Pyruvate is
transported into the mitochondrion. It is further broken down, and an acetyl group from
the pyruvate enters the citric acid cycle (also called the Krebs cycle). Four products are
formed: NADH, FADH2, CO2, and GTP. NADH and FADH2 are electron carriers that will
eventually donate their electrons to the electron transport chain. The ability of NADH to
donate electrons is shown in Figure 14-9. CO2 is a waste product. GTP is a high-energy
molecule that is usually converted to ATP.
A Chemiosmotic Process Converts Oxidation Energy into ATP
!An overview of oxidative phosphorylation is shown in Figure 14-10. This is a
very important figure. Make sure you understand it before reading the rest of the chapter.
Here’s what happens:
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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
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