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Gerald Karp
Cell and Molecular Biology
Fifth Edition
CHAPTER 5 Part 1
Aerobic Respiration
and the Mitochondrion
Copyright © 2008 by John Wiley & Sons, Inc.
5.1 Mitochondrial
structure and function

1. Living fibroblast
2. TEM
3. Sperm midpiece
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1-4μm, 0.2- 1.0μm
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1. Mitochondrial membranes
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The outer membrane is thought to be
homologous to an outer membrane
present as part of the cell wall of
certain bacterial cells.
The inner membrane is highly
impermeable; all molecules and ions
require special membrane transporters
to gain entrance to the matrix.
2. The mitochondrial matrix

Possess ribosomes, circular DNA to
manufacture their own RNAs and
proteins
5.2 Oxidative metabolism in
the mitochondrion
An overview of carbohydrate metabolism in eukaryotic cells


Pyruvate + HS-CoA + NAD+ → acetyl
CoA + CO2 + NADH + H+
In matrix
1. The Tricarboxylic Acid (TCA)
cycle

Acetyl CoA + 2 H2O + FAD + 3 NAD+ +
GDP + Pi → 2 CO2 + FADH2 + 3 NADH
+ 3H+ + GTP +HS-CoA
The glycerol phosphate shuttle

Electrons are transferred from NADH to
dihydroxyacetone phosphate (DHAP) to
form glycerol 3-phosphate, which
shuttles them into the mitochondrion.
These electrons then reduce FAD at the
inner membrane, forming FADH2 which
can transfer the electrons to a carrier of
the electron-transport chain.
An overview of carbohydrate metabolism in eukaryotic cells
2. The importance of reduced
coenzymes in the formation of
ATP (Chemiosmosis)

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1. High-energy electrons are passed
from FADH2 or NADH to the first of a
series of electron carriers in the
electron transport chain.
2. The controlled movement of protons
back across the membrane through an
ATP-synthesizing enzyme provides the
energy required to form ATP from ADP.
A summary of the process of oxidative phosphorylation
5.3 The role of mitochondria
in the formation of ATP

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1. Electron transport
2. Oxidation-reduction potentials
3. Types of electron carriers
1. Oxidation –reduction potential
Oxidizing agents can be ranked in
a series according to their affinity
for electrons:
the greater the affinity, the stronger the
oxidizing agent.
Reducing agents can also be
ranked according to their affinity
for electrons:


The lower the affinity, the stronger the
reducing agent
Reducing agents are ranked according
to electron-transfer potential, such as
NADH is strong reducing agent,
whereas those with low electrontransfer potential such as H2O, are
weak reducing agents.
Oxidizing and reducing agents occur
as couples such as NAD+ and NADH.
Strong reducing agents are coupled
to weak oxidizing agents and vice
versa.
For example,
in NAD+ - NADH, NAD + is a weak
oxidizing agent,
in O2 – H2O, O2 is a strong oxidizing agent
The affinity of substances for
electrons can be measured by
instruments that detect voltage—
oxidation-reduction (redox)
potential.
2. Electron transport

1. Five of the nine reactions in matrix in Fig.
5.7 are catalyzed by dehydrogenases that
transfer pairs of electrons from substrates to
coenzymes, NADH and FADH2 → electron-
transport chain

2. NADH and FADH2 dehydrogenase are
located in the inner membrane of
mitochondria.
3. Types of electron carriers
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Flavoproteins
Cytochromes
Ubiquinone
Iron-sulfur proteins
Electron-transport complexes
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1. Complexes I, II, III, IV ----Fixed in place
2. I, III, VI in which the transfer of electrons
is accompanied by a major release of free
energy.
2. Ubiquinone (lipid-soluble), cytochrome c
(soluble protein in the intermembrane space)---move within or along the membrane
I, III, VI are described as proton pump which drive the production of ATP.
5.5 The mechinery for ATP
formation

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1. The structure of ATP synthase
2. The basis of ATP formation according
to the binding change mechanism
3. Other roles for the proton-motive
force in addition to ATP synthesis
RECALL THAT:
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1. Enzymes do not affect the
equilibrium constant of the reaction
they catalyze
2. Enzymes are capable of catalyzing
both the forward and reverse reactions
Mammalian liver
has Ca 15000
copies of ATP
synthase.
Homology are
found in the
bacterial plasma
membrane, inner
membrane of
mitochondria, and
thylakoid
membrane
F1 : head (90A) in
matrix
F0: basal region
embedded in the
inner membrane
The structure of
ATP synthase
2. The basis of ATP formation
according to the binding change
mechanism

1979 Paul Boyer (UCLA): published a
hypothesis “ binding change mechanism”
Using the proton gradient to
drive the catalytic machinery:
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1. What is the path taken by protons as
they move through the F0 complex?
2. How does this movement lead to the
synthesis of ATP?
3. The role of the F0 portion of ATP
synthase
All of the following presumptions were
confirmed by data collection between
1995-2001
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1. The c subunit of the F0 base were assembled into
a ring that resides within the lipid bilayer.
2. The c ring is physically bound to the γsubunit of
the stalk.
3. The “downhill” movement of protons through the
membrane drives the rotation of the ring of c subunit.
4. The rotation of the c ring of F0 provides the twisting
force that drives the rotation of the attached γsubunit,
leading to the synthesis and release of ATP.
“Seeing is beliving”


Masasuke Yoshida et al. at the Tokyo
Institute Technology in Japan
They devised an system to watch the
enzyme catalyze the reverse reaction
from the normally operating cell.
Only two biological structures are
known that contain rotating parts
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1. ATP synthase
2. Bacterial flagella
3. Both are described as rotary
“nanomachines”
4. Invent nanoscale devices
5. Someday, human may be using ATP
instead of electricity to power some of
their most delicate instruments.
Rotation of the c ring drives rotation
of the attached γsubunit
H+ movements drive the
rotation of the c ring
4. From the middle of the “a”
subunit into the matrix
1. Each “a” subunit
has two halfchannels that are
physically separate
2. From intermembrane
space into “a” subunit
3. Binding of the H+
to the carboxyl
group of aspartic
acid generates a
major
conformational
change in the c
subunit to rotate 30o
in a Counterclockwise direction.
1. one H+ would remove the ring 30o
2. In this case, the association/dissociation of 4
protons in the manner described would move the
ring 120o.
3. This would drive a corresponding rotation of the
attached γsubunit 120o and lead to release newly
synthesized ATP.
4. The translocation of 12 protons would lead to
the full 360orotation of the c ring and γunit and
synthesis of 3 molecules of ATP.
Other roles for the proton-motive
force in addition to ATP synthesis