ENERGY

1
ENERGY
Work (force x distance)
Light (hn)
Heat
CHEMICAL
chemical bond energy (high-energy bonds)
electrochemical energy (oxidation-reduction)
gradients (proton gradients)
2
POLYSACCHARIDES (COMPLEX CARBOS)
glucose
Glycolysis
2 NADH
ATP
pyruvate
acetyl-CoA
FADH2 and NADH (reducing power)
O2
citric acid cycle
oxidative phosphorylation
ATP
ATP
ATP
ATP
ATP
3
FAD (Flavin Adenine Dinucleotide), a coenzyme
reactive center
vitamin B2
H
H
FAD
FADH2
C
C
R
R
H
H
Coenzymes-small organic molecules (often
derivatives of vitamins) that function with
enzymes during catalysis. Some are bound
covalently to the enzyme, while others act more
like a substrate
4
NAD (Nicotinamide Adenine Dinucleotide)
reactive center
H
H
H
..
N
NAD
NADH



NAD
NADH
H
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Standard Reduction Potential, Eo
Redox Potential is a measure of how readily
an electron donor (reductant) gives up electrons
to an electron acceptor (oxidant).
Thus, for a given redox reaction, electrons flow
from the reductant in the redox pair with
the lowest standard redox potential (Eo) to the
oxidant of the pair with the highest Eo
Standard reduction potentials of important
biological redox pairs
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example
lactate NAD
pyruvate NADH H
from table
lactate
pyruvate 2H 2e-
Eo -0.19 V
NADH H
NAD 2H 2e-
Eo -0.32 V
DEo Eo (acceptor) - Eo (donor)
-0.19 V - (- 0.32 V) 0.13 V
In this example, NADH is the electron donor and
pyruvate is the electron acceptor (because the
NAD/NADH pair has a lower Eo than the
pyruvate/lactate pair and therefore NADH has a
lower affinity for electrons than lactate)
The standard potential can be converted to free
energy available for a redox reaction DG
-nF DEo
DG -nF DEo - 2 (23 kcal) (0.13 V) -
0.6 kcal/mol
V mol
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increasing redox potential
entry point for NADH
entry point for FADH2 (complex II)
the electron transport chain consists of
four enzymatic complexes (I-IV) in the IMM,
linked by two mobile electron carriers (Coenzyme
Q and cytochrome C)
electron-carrying groups in the chain are
chemically diverse and include flavins,
iron-sulfur centers, heme iron (cytochromes),
ubiquinone (coenzyme Q)
the chain is organized in a series, such that the
electron carriers in the complexes are linked in
order of increasing redox potential (negative to
positive)
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Clinical Correlation
Cyanide Poisoning
CN binds to Fe3 in the heme of cytochrome a,a3
component of complex IV and prevents O2 reduction
(terminal step of electron transport)
mitochondrial respiration and ATP production
cease leading to rapid cell death. Death occur
from tissue asphyxia, especially in the CNS.
Treatment 1. pray for victim because CN is one
of the most potent and rapidly acting poisons
known. 2. If caught early, Nitrites will
convert Fe2 in hemoglobin into Fe3 and compete
for binding of CN to complex IV. 3. In
addition, administration of thiosulfate will
allow enzymatic conversion of CN to thiocyanide
(which is non-toxic).
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-16.6 kcal/mol
-8.8 kcal/mol
-26.7 kcal/mol
there are three points (at complex I, III and IV)
where a potential difference drop is more than
great enough (that is, DG is negative enough)
to provide the free energy required for ATP
synthesis.
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Chemiosmotic-coupling mechanism (the Mitchell
hypothesis, Nobel Prize)
basic features
1. During electron transport, energy derived
from large redox potential changes (DE) is used
to translocate protons across the IMM to form an
electrochemical gradient. There are
two contributing factors to the total energy in
this gradient, the membrane potential (0.14 V)
due to charge separation of and the pH gradient
(H concentration gradient) equivalent to 0.84
volts, giving a total proton motive force of
0.224 volts. In free energy terms, this is 5.2
kcals/mol of protons. 2. This stored energy
(like a battery in many ways) can subsequently
be converted into chemical bond energy by
the mitochondrial proton-translocating ATP
synthase in the form of a phosphodiester bond in
ATP. This process is called oxidative
phosphorylation (or OXPHOS). 3. Electron
transport and ATP production are
functionally coupled, that is inhibition of one
leads to inhibition of the other (this is often
referred to as respiratory control).
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matrix (higher pH, lower H)
intermembrane space (lower pH, higher H)

• uncouplers exist in equilibrium between
• a protonated and un-protonated form, of
• which the protonated is membrane -permeable
• pH gradient across IMM favors one form over
• the other

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coupling is demonstrated in studies
using chemical uncouplers and inhibitors of OXPHOS
succinate
ADP
oligomycin
2,4-dinitrophenol (DNP)
O2 0
oligomycin- direct inhibitor of the mitochondrial
ATP synthase, prevents phosphorylation of ADP to
ATP
DNP- a chemical uncoupler, a compound that
carries protons across the IMM and dissipates the
proton gradient, thereby preventing ATP synthesis
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structure of the ATP synthase (Walker, Nobel
Prize)
total of 10 different types of subunits (two of
which are mtDNA encoded) total mw 450 kDa
oligomycin binds in Fo portion and
inhibits proton translocation
binding-change catalytic mechanism
F1 exists in three inter-convertible
conformations loose (L), tight (T) and open (O).
Catalysis is a simple three-step program. Step
1. binding of ADP and Pi to L. Step 2. free
energy from proton translocation drives large
conformational changes to convert L to T, T to
O, and O to L. Step 3. synthesis of ATP at T site
and release of ATP from O site.
http//www.sp.uconn.edu/7Eterry/images/movs/synth
ase.mov
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cytosolic side
matrix side
IMM
ADP
ATP
adenine nucleotide transporter (ANT)
adenine nucleotides do not diffuse freely
across the IMM, therefore must be shuttled by the
ANT
exchange is energetically expensive because
it decreases the membrane potential (ATP4- out
for ADP3- in is a net loss of positive charge on
the cytoplasmic side). This works against
proton pumping out.
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Clinical Correlation
OXPHOS-related disorders (mtDNA mutations)
human mtDNA 16.6 kb
maternally inherited
100 -10,000 copies/cell
mtDNA mutations cause human disease due to loss
of expression of some or all of the 13
mtDNA-encoded subunits of OXPHOS complexes
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LSP
HSP
human mtDNA
1. transcription
2. RNA processing
1 mRNA
12 mRNAs
2 rRNAs
8 tRNAs
14 tRNAs
3. mitochondrial translation
I
IV
V
III
II