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5.1 Mitochondrial structure
and function
• 1. Living fibroblast
• 2. TEM
• 3. Sperm midpiece
• 1-4μm, 0.2- 1.0μm
1. Mitochondrial membranes
• 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.
5.1 Mitochondrial structure
and function
• 1. Living fibroblast
• 2. TEM
• 3. Sperm midpiece
• 1-4μm, 0.2- 1.0μm
1. Mitochondrial membranes
• 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.
• Possess ribosomes, circular DNA to
manufacture their own RNAs and proteins
5.2 Oxidative metabolism in the
mitochondrion
• Pyruvate + HS-CoA + NAD+ → acetyl CoA
+ CO2 + NADH + H+
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.
2. The importance of reduced
coenzymes in the formation of
ATP (Chemiosmosis)
• 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.
5.3 The role of mitochondria in
the formation of ATP
• 1. Oxidation-reduction potentials
• 2. Electron transport
• 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 electron-transfer potential such as
H2O, are weak reducing agents.
Oxidizing and reducing agents occur
as couples such as NAD+ and NADH
which differ in their electrons.
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 Fig. 5.7
are catalyzed by dehydrogenases that
transfer pairs of electrons fron
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
•
•
•
•
•
•
Flavoproteins (FMN of NADH dehydrogenase)
Cytochromes (heme group)
Three copper atoms
Ubiquinone (Coenzyme Q)
Iron-sulfur proteins
With the exception of ubiquinone, all of the redox centers
within the respiratory chain that accept and donate
electrons are prosthetic groups (non-amino acid
components that are tightly associated with proteins)
Electron-transport complexes
• 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
Experimental demonstration that
cytochrome oxidase is a proton pump
Translocation of protons and the
establishment of a proton-motive force
• Concentration difference between hydrogen ions
between the inside and outside of the membrane (∆ pH)
• Voltage difference (Ψ)that results from the separatopn of
charge across the membrane
• Electrochemical gradient → proton motive force (∆p)
• ∆p = Ψ-2.3 (RT/F)∆ pH
• The permeability of the inner membrane to
Cl ions
• Uncoupling proteins (UCP)
5.5 The mechinery for ATP
formation
• 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:
• 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
2. The basis of ATP formation
according to the binding change
mechanism
• 1979 Paul Boyer (UCLA): published a
hypothesis “ binding change mechanism”
“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
• 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.
Using the proton gradient to
drive the catalytic machinery:
• 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 19952001
• 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.
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. Movement of the ring is driven by the
conformational changes associated with the
sequential protonation and deprotonation of the
aspartic acid residue of each “c” subunit.
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
GLYOXYSOME IN PLANT
SEEDLINGS
• 1. conversion of stored fatty acids to
carbohydrate
• 2. disassembly of stored fatty acids
generates acetyl CoA, which condenses
with oxaloacetate to form citrate, which is
then converted into glucose by a series of
enzymes of the glyoxylate cycle localized
in the glyoxysome.