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Blueprint Series

Complete Solution
Chapter 12

12
CELLULAR ENERGETICS

REVIEW THE CONCEPTS
1
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Like ATP,
the pmf is a form of stored energy, and the energy stored in the pmf may be converted
to ATP by the action of ATP synthase
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At high doses, DNP can be fatal
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Similarities between bacteria, mitochondria, and chloroplasts reflect the pro-posed
endosymbiotic origin of mitochondria and chloroplasts
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Bacterial
and mitochondrial ribosomes are sensitive to chloramphenicol but resistant to cycloheximide
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Also, comparing the mitochondrial DNA of multiple classes of
eukaryotes, both unicellular and multicellular, all can be seen to derive from a common ancestor with a genome similar to contemporary symbiotic bacteria that invade
host eukaryotic cells
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45

3
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The cristae increase
the surface area of the inner membrane, thereby increasing the total amount of
membrane and hence electron-transport chain components: ATP synthase molecules and transporters of reagents and products of the citric acid cycle and
oxidative phosphorylation are all increased
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Finally, cardiolipin enhances the barrier properties of the inner membrane by reducing the membrane’s permeability to protons
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Glycolysis does not require oxygen, but the citric acid cycle and the electrontransport chain do require oxygen to function
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For electron transport,
oxygen is required as an electron acceptor
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5
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When oxygen is present, the electrons
of this electron carrier are eventually donated to the electron-transport chain in
oxidative phosphorylation
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Fermentation reactions oxidize NADH, replenish the store of NAD+,
and thus allow glycolysis to continue
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Electrons are passed to the electron carrier NADH in the cytoplasm
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NADH molecules can freely pass
through the outer mitochondrial membrane through the channel protein, porin,
which allows free passage of small molecules
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Instead, electron shuttles, such as
the malate-aspartate shuttle, indirectly transfer electrons via intermediates that
shuttle back and forth across the inner membrane
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Fatty acids are oxidized in the mitochondria and the persoxisome, but unlike
the mitochondria, oxidation in the peroxisome does not generate ATP
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In the
case of the human genetic disease X-linked adrenoleukodystrophy (ALD), however, this oxidation is defective because the ATP-binding cassette (ABC) ABCD1
transporter, localized to peroxisome membranes, is unable to import very long
chain fatty acids into this organelle
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8
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Several types of heme, an

iron-containing prosthetic group, are associated with the cytochromes
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9
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As
this occurs, the electrons undergo a drop in electrical potential
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Respiration supercomplexes
would be an efficient way to quickly pass electrons from one complex to the next,
increasing the speed at which the process could occur
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CoQ functions within the
inner membrane, bringing electrons to complex III
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This is only possible because CoQ is soluble within
the membrane bilayer
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The underlying reason for the difference in ATP yield for electrons donated
by FADH2 and NADH is that the electrons carried in FADH2 have less potential
energy (43
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6 kcal/mol)
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11
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F0 is embedded in the
mitochondrial inner membrane, and it is through this component that protons
travel from one side of the inner membrane to the other, as they move down
their electrochemical gradient
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One of its subunits is responsible for nucleotide binding, interacting with ADP and Pi molecules, and releasing ATP following its formation
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This build-up of protons results in a pH
decrease in the vesicle lumen
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12
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Glycolysis and the citric acid cycle take place in the bacterial cell cytosol,
while electron-transport components are localized to the bacterial plasma membrane
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In addition to using the pmf to synthesize ATP, aerobic bacteria also use the pmf to power uptake of certain nutrients
and cell swimming
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In addition to providing energy to power ATP synthesis, the pmf also provides
the energy used by several active transport proteins to move substrates into the

mitochondria and products out of the mitochondria
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14
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In mitochondria, the specific
complex is the CoQH2-cytochrome c reductase complex, while in chloroplasts it
is the cytochrome bf complex, and in purple bacteria it is the cytochrome bc1
complex
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Next, one electron
is transported directly to cytochrome c while the other partially reduces a CoQ
molecule bound to the Qi site on the inner side of the complex, forming a CoQ
semiquinone anion
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As before, one electron is transferred to cytochrome c, but the
other combines with the CoQ semiquinone anion at the Qi site to produce
CoQH2, thus regenerating one CoQH2
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15
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While ATP is generated in photosynthesis, this energy is used to create
sugars, which the cells use in a variety of different processes (including respiration)
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The prokaryote and eukaryote developed a symbiotic relationship
and eventually the prokaryote lost its independence
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6CO2 + 6H2OD6O2 + C6H12O6 O2-generating photosynthesis uses the
energy of absorbed light to create, via electron donation to quinone, the powerful oxidant P+ form of the reaction center chlorophyll
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The electrons are then passed
along an electron-transport chain, and the stored energy is converted to other
forms for subsequent use in ATP synthesis and carbon fixation
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17
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During stage 1, which occurs in the thylakoid membrane, light is absorbed by the reaction center chlorophyll, a charge
separation is generated, and electrons are removed from water, forming oxygen
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During stage 3, protons move down their electrochemical gradient across the thylakoid membrane through F0F1 complexes

and power ATP synthesis
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CO2 fixation occurs in the stroma and
carbohydrate (sucrose) synthesis occursin the cytosol
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Chlorophyll a is present in both reaction centers and antenna
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Antennas capture light energy and
transmit it to the reaction center, where the primary reactions of
photosynthesis occur
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19
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Theseorganisms still utilize photosynthesis to produce ATP by
utilizing cyclic electronflow to produce a pmf (but no oxygen or reduced
coenzymes), which can be uti-lized by F0F1 complexes
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For linear elec-tron flow, hydrogen gas
(H2) or hydrogen sulfide (H2S) rather than H2O donateselectrons, so no
oxygen is formed
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PSI is driven by light of 700 nm or less and its primary function is to
transfer electrons to the final electron acceptor, NADP+
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During linear electron flow,
electrons move as follows: PSII (water split to produce
electrons)Dplastoquinone (Q)Dcytochrome bf
complexDPlastocyaninDPSIDNADP+
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21
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The mechanism of inactivation
depends on theenzyme; examples include pH-dependent and Mg2+dependent enzyme regula- tion, as well as reversible reduction-oxidation
of disulfide bonds within certain Calvin cycle enzymes
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Rubisco (ribulose 1,5-bisphosphate carboxylase) is a large enzyme present
in the stromal space of the chloroplast
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