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Biochemistry - Exam 4

Terms in this set (127)

These six amino acids are split between two subunits. Together, they form a ____ that appears to ____. Mutation of several of these residues to Ala results in a significant decrease in the decarboxylation activity of the enzyme. researchers propose that this region may be important for ____ between the two active sites to ensure that only one is catalytically active at a time
acidic tunnel; connect the two active sites; proton shuttling
What compound is the reactant reduced in reaction 8 of the citrate cycle?
NAD+
What compound is the reactant oxidized in reaction 8 of the citrate cycle?
malate
What compound is converted to citrate by citrate synthase in reaction 8 of the citrate cycle?
oxaloacetate
What statements are true in regard to the citrate synthase reaction?
the histidine residue would hydrogen bond to acetyl-CoA throughout the reaction mechanism, stabilizing the enolate intermediate

mutating histidine residue 274 of the citrate synthase enzyme to an alanine amino acid would likely eliminate or reduce the enzymatic activity of citrate synthase

oxaloacetate would be repulsed from aspartic acid in the first step of the reaction mechanism
The reaction catalyzed by succinyl-CoA synthetase is a reversible reaction. What would be the first step in this mechanism moving in the direction toward the formation of succinyl-CoA, GDP, and Pi from succinate, GTP, and CoA
reaction initiated by histidine lone pair to form phosphohistidine
What is a negative effector for pyruvate dehydrogenase kinase?
Ca2+
Which of the following is responsible for the production of GTP in the citrate cycle?
succinyl-CoA synthetase
Beriberi results from a deficiency in which of the following vitamins?
thiamine
Which of the following is true regarding the iron-sulfur cluster?
the iron-sulfur cluster of aconitase coordinates an OH removal and a hydration reaction
In the citric acid cycle, the enzyme succinate dehydrogenase catalyzes a reversible reaction using FAD/FADH2 as an oxidizing/reducing agent. Which of the following statements best explains how the redox component of this reaction contributes to the reaction's ability to be reversible under cellular conditions?
the change in the biochemical standard reduction potential is small
If the succinate dehydrogenase enzyme were mutated such that NAD+ was able to function as the cofactor instead of FAD, how would this change affect the spontaneous direction under standard conditions and the potential reversibility of the reaction under cellular conditions?
the reaction would likely be irreversible under cellular conditions

fumarate reduction would be spontaneous under standard conditions
Which of the following diffuses throughout the inner mitochondrial membrane to carry electrons between complexes in the electron transport system?
coenzyme Q
What coenzyme is used by pyruvate carboxylase?
biotin
You prepare your experiment by mixing the three components (artificial membrane, bacteriorhodopsin, and ATP synthase) in a test tube plus ADP and 32Pi and look for ATP accumulation by spectroscopy; however, after an hour of waiting, you find nothing at all. Racker and Stoeckenius assured you that placing the membranes in high-pH media wasn't necessary as long as you did "this" . . . but you can't remember what "this" was exactly. What should you have done?
your sample was left in the dark and must be exposed to light for the proton gradient to be generated if samples aren't immersed in high-pH buffer
As part of the troubleshooting process, you decide to investigate whether a proton gradient is present across the artificial membranes in your test tube. When comparing proton concentrations and membrane potentials (Δψ), which of the following would be evidence of a properly formed proton gradient?
inside the vesicle we have a higher [H+] and a more positive membrane potential, Δψ, compared to the outside of the vesicle
You are finally getting your experiment to work now and have accumulated quite a bit of ATP in the surrounding solution. You decide to test the hypothesis that the ATP synthase can work in reverse, breaking ATP down to ADP and Pi instead of synthesizing it. How might you need to modify your experiment to test your hypothesis?
Lower the pH of the surrounding solution
In Part 1, it is shown that succinyl-CoA is an inhibitor for the citrate synthase reaction. However, acetyl-CoA is not listed as an inhibitor for the α-ketoglutarate dehydrogenase reaction. What is a reasonable explanation for this apparent contradiction?
The concentration of acetyl-CoA is unlikely to have a significant effect on α-ketoglutarate dehydrogenase activity as compared to the concentration of succinyl-CoA
After robust lipid breakdown by the cell, there could be an increase in the rate of...
the citrate cycle

amino acid synthesis

carbohydrate synthesis
Concerning proton movement in mitochondria and chloroplasts, the ____ have a ____ H+ concentration
intramembrane space in mitochondria; high
The reaction catalyzed by malate dehydrogenase has a ΔG°' = 29.3 kJ/mol, while the actual ΔG' under cellular conditions is very close to equilibrium. As NADH rises, this reaction will become more favorable in the direction of oxaloacetate reduction. A student studying this reaction wishes to calculate the specific [NADH]/[NAD+] required to push the reaction in this direction under cellular conditions. What would you explain to this student regarding the different factors that have to be considered in order to be able to perform such a calculation?
considering only biochemical standard state values and cellular concentrations for the malate dehydrogenase reaction would be insufficient to fine the correct ratio
What is the net result from the electron transport system?
reduction of molecular oxygen
Oxaloacetate is transported both into and out of the mitochondrial matrix via what molecule?
malate
What statement concerning ATP, ADP, and Pi transport across the inner mitochondrial membrane is correct?
transport of H2PO4 via phosphate translocase is electrically neutral
What is the overall ATP yield from a molecule of glucose in liver cells?
32
In the ATP synthase complex, the α subunit is shown in magenta and the β subunit in green. The location of the ATP synthase complex active site can be best described as being found
at the interface between the α and β subunits
In the ATP synthase complex, three amino acid side chains and ANP are interacting with a single Mg2+ atom. Zoom in on each enzyme-derived amino acid side chain and identify the amino acids. Remember that carbon atoms are shown in gray and oxygen atoms in red. What amino acids are shown to be interacting with Mg2+?
one threonine and two glutamates
What enzyme is crucial for transfer of electrons from cytosolic NADH into the mitochondrial matrix in muscle cells?
glycerol-3-P-dehydrogenase
What is an inhibitor of complex IV?
cyanide
In each of the three catalytic sites of the yeast ATP synthase, three amino acid residues bind an essential Mg2+ ion. What mutation would likely reduce the activity of the ATP synthase?
E189A
Why was ANP used in the experiment that generated the image above of yeast ATP synthase?
ANP is nonhydrolyzable and will "freeze" the desired conformation of the protein
How would a mutation of Asp59 in the c subunit to lysine (Lys) affect the function of the ATP synthase complex?
the c subunit would be unable to accept a proton from the a subunit half-channel, and the γ subunit would not be able to rotate, rendering the complex nonfunctional
List stator subunits
a, d, OSCP, b, h
List rotor subunits
c, γ,...
List headpiece subunits
α, β
What subunit rotates in response to the flow of protons through F0?
γ
In what order would malate-aspartate shuttle enzymes need to function in order to facilitate transfer of an electron pair from the cytosol to the mitochondrial matrix in liver cells?
(1) cytosolic malate dehydrogenase, (2) mitochondrial malate dehydrogenase, (3) mitochondrial aspartate aminotransferase, (4) cytosolic aspartate aminotransferase
What is the primary purpose of the malate-aspartate shuttle?
to move electrons from NADH in the cytosol to the mitochondrial matrix, because the mitochondrial membrane is impermeable to NADH
Aspartate aminotransferase, or AST, is measured clinically in liver function tests, and there are some clinical conditions where AST activity has negative implications. For instance, AST has been identified as a potential selective target of breast cancer chemotherapies. Considering what you've learned, what would be the most likely consequence of inhibiting mitochondrial AST?
anaerobic metabolism through glycolysis would be inhibited, because there would be less NAD+ regenerated in the cytosol than if AST were functioning
In the figure above, oxygen consumption and ATP synthesis increase with the addition of succinate and ADP + Pi. Which of the following will have to accept electrons from succinate in order for oxidative phosphorylation to occur?
complex II
Thermogenin differs from 2,4-dinitrophenol in that thermogenin...
acts in a cell-specific manner because it is a protein
Choose the ONE best answer explaining how oxaloacetate and acetyl-CoA levels are balanced to maximize flux through the citrate cycle when energy charge in the cell is low.
pyruvate dehydrogenase is activated by CoA, but inhibited by its product acetyl-CoA, whereas pyruvate carboxylase is activated by acetyl-CoA to produce more oxaloacetate for the citrate synthase reaction
What two molecules function as electron acceptors in the citrate cycle?
NAD+, FAD
Identify the strongest oxidant (a) and strongest reductant (b) in the table below
(a) O2 (b) ferredoxin
What correct statements describe the citrate cycle?
the pool of mitochondria oxaloacetate can be increased by pyruvate

ATP is an indirect product of the citric acid cycle
What is the pyruvate dehydrogenase reaction regulated by?
allosteric control and covalent modification
Although both pyruvate dehydrogenase and glyceraldehyde 3-phosphate dehydrogenase use NAD+ as their electron acceptor, the two enzymes do not compete for the same cellular NAD pool because...
pyruvate dehydrogenase is located in the mitochondrion, and glyceraldehyde 3-phosphate dehydrogenase in the cytosol
In two turns of the citrate cycle originating from oxidation of 2 moles of acetyl-CoA, how many electrons are transferred from the citrate cycle intermediates to NAD+ and FAD?
16
What role do vitamins have in the pyruvate dehydrogenase reaction?
vitamin B3 is a critical component of not only the PDH complex, but also the alpha-ketoglutarate dehydrogenase complex, an enzyme in the citrate cycle

riboflavin is an electron carrier that functions in a redox reaction involving dihydrolipoamide

vitamin B5 functions as an acetate carrier using a high energy thioester bond formed in the E2 catalytic site

vitamins provide functional chemical groups in all three subunits of the PDH protein complex
Regeneration of NAD+ and FAD inside the mitochondrial matrix is required because...
they maintain flux through the citrate cycle
How would an increased level of acetyl-CoA be expected to affect the pyruvate dehydrogenase reaction?
the pyruvate dehydrogenase kinase enzyme activity would increase, resulting in an inhibition of pyruvate dehydrogenase activity
The disease beriberi is caused by a nutritional deficiency in vitamin B1 (thiamin). What key mitochondrial enzyme uses thiamin as a coenzyme in a reaction that generates acetyl-CoA, CO2, and NADH + H+ as products; and why is this condition rare in developed countries?
pyruvate dehydrogenase; beriberi is rare because many common foods are vitamin-fortified
If acetyl-CoA is not metabolized by the citrate cycle, its most likely metabolic fate is...
used to synthesize fatty acids
A good reason to refer to the metabolic cycle discovered by Hans Krebs as the citrate cycle is...
the three carboxylate groups are deprotonated under physiological conditions, and therefore do not function as acids
The primary function of the citrate cycle is to oxidize...
acetate
What enzyme does the condensation reaction catalyze?
citrate synthase
What enzyme does the dehydration reaction catalyze?
aconitase
What enzyme does the oxidative decarboxylation reaction catalyze?
isocitrate dehydrogenase
What enzyme does the substrate level phosphorylation reaction catalyze?
succinyl-CoA synthetase
What enzyme does the dehydrogenation reaction catalyze?
malate dehydrogenase
What is the biochemical explanation for the observed toxic effects of arsenic contaminated well water in Bangladesh?
arsenic is converted to arsenite, which covalently modifies reduced lipoamide, thereby inhibiting activity of the pyruvate dehydrogenase complex and blocking conversion of pyruvate to acetyl-CoA

the arsenic contaminated well water caused inhibition of dihydrolipoyl transacetylase, which is an enzyme subunit required for metabolism of rice starch, the source of 70% of their daily caloric intake
Calculate the change in standard reduction potential, delta Eº', of a coupled redox reaction involving O2 and ferredoxin (Fe2+) using the table below
+1.25V
The purpose of the first three steps in the pyruvate dehydrogenase reaction is to...
form acetyl-CoA
The regulatory mechanism in the citrate cycle involving the NADH to NAD+ ratio is considered to be an example of regulation by...
product inhibition
What three of the molecules listed below are derived directly from citrate cycle intermediates?
glutamate, aspartate, and d-aminolevulinic acid
When the citrate cycle is inhibited, which two metabolites are exported to the cytosol for fatty acid and cholesterol synthesis?
citrate and malate
What statement comparing chloroplasts and mitochondria is true?
chloroplasts and mitochondria use energy from a proton gradient to make ATP
The ultimate electron acceptor of the mitochondrial electron transport system is...
O2
Approximately how many more ATPs are made from one glucose molecule under aerobic conditions with oxidative phosphorylation than under anaerobic conditions limited to glycolysis?
30
What is the structural component of the yeast ATP synthase that synthesizes ATP?
the headpiece containing three α and three β-subunits
The drug oligomycin inhibits ATP synthase by preventing protons from flowing through the enzyme. Oligomycin must bind to the ____ of ATP synthase
F0 subunit
What would happen if mitochondria were treated with a proton gradient uncoupler, such as 2,4-dinitrophenol?
protons would be pumped by the mitochondrial electron transport chain, although no ATP would be synthesized
What is the driving force for ATP synthesis by the ATP synthase enzyme?
the pH gradient across the inner mitochondrial membrane
What would happen to a mutated ATP synthase enzyme where the proton binding aspartate residue on the c subunits was mutated to a lysine?
the rotor would not rotate and ATP would not be synthesized
How many degrees of rotation by the gamma subunit occur for 1 ATP synthesized by T. hotsynthaseii?
180
Considering that 10 H+ are translocated per NADH oxidized by T. hotsynthaseii electron transport system, is this ATP synthase more efficient, less efficient, or the same efficiency as most organisms?
less efficient
What is the difference in standard free energy for the reduction of O2 when oxidizing FADH2 as compared to oxidizing NADH?
-55 kJ/mol
Considering that oxidative phosphorylation is only about 70% efficient, what is the actual difference in the change in standard free energy available for ATP synthesis when comparing NADH oxidation to FADH2 oxidation?
-38.5 kJ/mol
How does this difference in standard free energy change between NADH and FADH2 oxidation explain the difference in ATP yield of ~2.5 ATP and ~ 1.5 ATP, respectively?
the energy required for ATP synthesis is ~40 kJ/mol in the cell, so ~1 ATP difference makes sense energetically.
How many ATPs are obtained from one acetyl-CoA run once through the citrate cycle, assuming that all resulting NADH and FADH2 is used by the electron transport chain and oxidative phosphorylation to make ATP?
10
An ATP synthase enzyme with more than 10 c subunits in the F0 stalk would...
require more protons to complete one 360 degree rotation
The mitochondrial ATP/ADP translocase is what type of transporter?
antiporter
Many mitochondrial diseases are passed on from parents to offspring...
through the mother only
What is the best way to explain how much energy is required to transport protons across the mitochondrial membrane as a function of energy available from redox reactions?
energy required to transport protons across the membrane is equal to the energy obtained from redox
How many protons (H+) are required for one complete (360°) turn of the catalytic head of yeast ATP synthase?
9
What experimental observation best explains the biochemical reason for the currency exchange ratio being 5 ATP/2 NADH in mitochondrial oxidative phosphorylation
the number of H+ translocated across the inner mitochondrial membrane for each NADH oxidized was determined and then divided by the number of H+ required to synthesize each ATP and transport in a Pi for each ATP generated
Inhibitors of the electron transport system, such as cyanide (CN−) and carbon monoxide (CO), inhibit complex IV by binding to the heme iron cofactor. What is the resulting effect on oxidative phosphorylation?
electron transport is disabled, and no protons are pumped
What are three true statements regarding the ATP synthase protein complex?
rotation of the c ring in the membrane is driven by protonation and deprotonation of an aspartate residue in the c subunit, because when the aspartate is protonated, it is now neutral instead of negatively charged and therefore is able to enter the hydrophobic membrane

the gamma subunit is asymmetric, therefore as it rotates in 120 degree steps in response to proton flow through F0, it makes 3 different contacts with the 3 beta subunits, thereby resulting in 3 different conformations of the beta subunits

in vitro, the ATP synthase can run in both directions. In one direction, ATP is synthesized as protons flow through the ATP synthase down their concentration gradient. In the other direction, ATP hydrolysis results in pumping of protons up their concentration gradient
What is the biochemical explanation for the lethal effects of dintrophenol (DNP) when ingested in large quantities for the purpose of losing weight?
DNP dissipates the proton gradient and severly reduces the efficiency of mitochondrial ATP synthesis, which causes liver damage due to accumulation of this hydrophobic molecule in membranes
Addition of carbon monoxide (CO) to an active in vitro suspension of mitochondria blocks the ETS by blocking electron transfer in complex IV.

a) What is one true statement regarding ATP synthase rates?

b) What is one true statement regarding oxygen consumption?
a) ATP synthesis rates will decrease because of decrease of the proton-motive force

b) ATP synthesis rates will decrease because of decrease of the proton-motive force
Which statement below is the most correct concerning the transport of ATP, ADP, and Pi across the mitochondrial inner membrane?
phosphate translocase functions as a symporter when transporting Pi and H+
List the six steps of the pyruvate dehydrogenase reaction
1. E1 subunit catalyzes the decarboxylation of pyruvate to form hydroxyethyl-TPP
2. Hydroxyethyl-TPP reacts with lipoamide in E2 to generate acetyl-dihydrolipoamide
3. Acetyl-dihydrolipoamide swings from E1 to E2 active site to generate acetyl-CoA from CoA
4. Dihydrolipoamide transfers 2 e-/2 H+ to form reduced dithiol and oxidized lipoamide.
5. Reduced dithiol in E3 transfers 2e-/2 H+ to E3-FAD to form E3-FADH2
6. FADH2 is oxidized in a coupled redox reaction to generate FAD and NADH
What human metabolic enzyme is most likely defective; and why is the lactate level so high in this patient?
succinate dehydrogenase; because pyruvate is converted to lactate
Which statement below bests describes the Chemiosmotic Theory proposed by Peter Mitchell?
Conversion of redox energy or light energy into potential energy as an electrochemical proton gradient
What type of transport protein is the mitochondrial ATP/ADP translocase?
an antiporter
Explain why a mutation in pyruvate carboxylase that blocks its ability to be regulated by acetyl- CoA results in lower rates of energy conversion via the Citrate Cycle
Oxaloacetate becomes limiting, reducing the rate of acetyl-CoA oxidation, which inhibits citrate cycle flux
How many protons are required to be transported into the mitochondrial matrix for every ATP that is synthesized and exported to the cytosol?
4 protons
How many protons are transported across the inner mitochondrial membrane for every NADH that is oxidized by Complex I the electron transport system?
10 protons
How many protons are transported across the inner mitochondrial membrane for every FADH2 that is oxidized by Complex II in the electron transport system?
6 protons
What explains the difference between number of ATP synthesized per NADH that is oxidized by the electron transport system compared to the number of ATP synthesized per FADH2 that is oxidized?
10/4 = 2.5 ATP/NADH and 6/4 = 1.5 ATP/FADH2
What inhibitor best represents the type of malfunction for a cracked canister?
FCCP
What inhibitor best represents the type of malfunction for a bent hose?
bonkrekic
What inhibitor best represents the type of malfunction for a broken handle?
rotenone
To make high levels of citrate to produce commercial grade citric acid, Pfizer modified culture conditions and used a special strain of Aspergillus niger to maximize fermentation. What two processes need to be inhibited in order to ensure the rate of citrate secretion exceeds citrate catabolism?
citrate cycle flux and the citrate lyase reaction
Which statement best describes the biochemical function of pyruvate carboxylase in regulating metabolic flux through the citrate cycle?
in the presence of high levels of acetyl-CoA, pyruvate carboxylase converts pyruvate to oxaloacetate
Pyruvate dehydrogenase (PDH) activity is controlled by phosphorylation such that PDH activity is decreased (T state) when it is phosphorylated. What enzyme increases PDH activity (R state)?
PDH phosphatase-1
How many H+ most likely flow through ATP synthase to generate 1 ATP?
4
How many degrees of rotation by the g subunit occur for 1 ATP synthesized by the bacterium?
90
Considering that 8 H+ are translocated per NADH oxidized by this bacterial electron transport system,
and the species contains a similar phosphate translocase as mitochondria, what is the ATP currency exchange ratio in terms of moles ATP synthesized for every mole NADH that is oxidized?
1.6
What is the biochemical mechanism by which ingesting 2,4-dinitrophenol (DNP) results in rapid weight loss by increased rates of metabolic flux through the fatty acid degradation pathway?
DNP uncouples electron transport from ATP synthesis and the body degrades stored fatty acids at a high rate to increase the energy charge
Why is it more accurate to call the pathway that converts acetyl-CoA to CoA + 2 CO2 the citrate cycle, rather than the tricarboxylic acid cycle (TCA), or simply the citric acid cycle?
because the primary product of reaction 1 in cells is citrate, which is a base not an acid at pH 7
An in vitro experiment used the isotope 14C-acetyl-CoA to identify 14C-oxaloacetate (OAA) as the final product of the citrate cycle. Explain why 14C-OAA could not be found when the reaction lacked Pi?
Pi is required in the succinyl-CoA synthetase reaction, which was inhibited, so no 14C-OAA is made
Identify the correct order of electron transfers in the electron transport system starting with the mitochondrial enzyme glycerol-3P dehydrogenase (GPDH) and ending with reduction of 1⁄2 O2
GPDH --> Coenzyme Q --> Complex III --> Complex IV --> 1/2 O2
Five coenzymes are needed for the pyruvate dehydrogenase (PDH) reaction. Name the three
that are covalently linked to proteins in the PDH complex
lipoamide, TPP, FAD
Which one of the statements below best describes the mechanism of proton translocation by the Electron Transport System using a redox loop mechanism exemplified by the Q cycle?
a redox reaction separating protons and electrons within complex III of the electron transport system, with the protons translocated to the inter-membrane space and the electrons used to reduce Q.
Why does cyanide, an inhibitor of Complex IV in the electron transport system, also block GTP synthesis in the mitochondrial matrix by inhibiting substrate level phosphorylation in the citrate cycle?
because without NAD+ produced by oxidation of NADH in Complex I, NAD+-dependent redox reactions in the citrate cycle are inhibited, thereby inhibiting the citrate cycle and blocking GTP synthesis
In 2 turns of the citrate cycle,...
a) how many electrons are transferred to NAD+?

b) how many CO2 are produced?

c) how many GTP are generated?
a) 12 electrons

b) 4 CO2

c)2 GTP
In the citrate cycle, the enzyme succinate dehydrogenase catalyzes a reversible reaction usingFAD/FADH2 as an oxidizing/reducing conjugate pair. Which of the following statements explains how the redox component contributes to the reversibility of this reaction?
the change in biochemical standard reduction potential is small
Considering that 22.4 kJ/mole is required to transport 1 H+ across the mitochondrial membrane, how much energy is available for proton translocation from the oxidation of FADH2 at Complex II?
134 kJ/mol
A desert plant was shown to have a differential pH gradient (DpH) across the chloroplast thylakoid membrane of 3.5 pH units relative to the stroma. What is the DG to transport 1 H+ across the thylakoid membrane from the stroma at 30oC given that the thylakoid membrane potential was below the level of detection and effectively 0 V?
+20.3 kJ/mol
The disease beriberi is caused by a nutritional deficiency in vitamin B1 (thiamin). What key mitochondrial enzyme uses thiamin as a coenzyme in a reaction that generates acetyl-CoA, CO2, and NADH + H+ as products; and why is this condition rare in developed countries?
pyruvate dehydrogenase; beriberi is rare because many common foods are vitamin fortified
What is the best way to explain how much energy is required to transport protons across the mitochondrial membrane as a function of energy available from redox reactions?
energy required to transport protons across the membrane is equal to the energy obtained from redox
The citrate cycle is considered the ____ of metabolism for three reasons, 1) it generates the bulk of ____ and ____ used in oxidative phosphorylation, the process that generates ____ per glucose, 2) it oxidizes a variety of ____ from different sources, and 3) it provides metabolites required for the biosynthesis of ____ acids
hub; NADH; FADH2; ATP; fuels; amino
Which molecular component of the electron transport system diffuses within the inner mitochondrial membrane to carry electrons collected from complexes I or II to complex III?
coenzyme Q
Pellagra, a niacin deficiency, was found in residents of Village A, but not in Village B. It was found that Village A prepares corn by boiling it in water to make porridge. However, in Village B, the corn is soaked in mineral lime (calcium hydroxide) before cooking it over an open flame using a flat iron skillet in the form of tortillas. Why do residents of Village A have pellagra, but not residents of Village B?
in Village B, niacin is released by alkali treatment and high heat and converted to NAD+/NADH
Select the one statement below best describing structure/function of the ATP synthase complex
the gamma subunit is asymmetric, therefore as it rotates in 120o steps in response to proton flow through Fo, it makes 3 different contacts resulting in 3 different conformations of the beta subunits
A desert plant was shown to have a differential pH gradient (DpH) across the chloroplast thylakoid membrane of 3.5 pH units relative to the stroma. What is the DG to transport 1 H+ across the thylakoid membrane from the stroma at 30oC given that the thylakoid membrane potential was below the level of detection and effectively 0 V?
+20.3 kJ/mol
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