Biochemistry Exam 2 Questions
In a hypothetical cell with regular electron transport chain and oxidative phosphorylation, the oxidation of each NADH molecule leads to the pumping of 10 protons from mitochondria matrix. If there are 10 c subunits in the transmembrane F0 subcomplex of the ATP synthase, 1) how many ATP molecules should be generated for each NADH oxidation (assuming 100% efficiency)? However, the cell only generates 2.5 ATP molecules through 1 NADH oxidation. 2) Provide at least one reason to rationalize such discrepancy in ATP production. The cell only generates 1.5 ATP molecules through 1 FADH2. 3) Calculate how many protons are pumped through Complex I of the electron transport chain. Show your calculations.
- 1) Three ATP molecules will be generated as 10 protons pass through 10 c subunits to complete one round of rotation. 2) Some protons can occasionally leak out of the inner mitochondria membrane and reduce the proton gradient, for instance through the uncoupling protein thermogenin. When the electrochemical potential gets high, the proton pumping process might also become less efficient. 3) Four protons are pumped through Complex I. Ten protons can generate 2.5 ATP, so four protons can generate 1 ATP molecule. The major energy efficiency difference between FADH2 and NADH is that Complex I pump protons. Complex I pump 4 protons to account for 1 ATP production difference.
The final product that is formed by the enzyme rubisco is:
3-phosphoglycerate
The final product that is formed by the enzyme rubisco is:
3-phosphoglycerate.
In the photolytic cleavage of water by the oxygen-evolving complex (2H2O --> 4H+ +4e- + O2), how many photons of light at a wavelength of 680 nm are required?
4
Although ATP synthesis requires both ADP and Pi, the rate of synthesis depends mainly on the concentration of ADP, not Pi. Why?
The steady‑state concentration of Pi in the cell is much higher than that of ADP.
which of the following is not a feature of complex IV?
in order to regenerate two water molecules, complex IV must go through catalytic cycle twice
During oxidative phosphorylation, the proton motive force that is generated by electron transport is used to: A) create a pore in the inner mitochondrial membrane. B) generate the substrates (ADP and Pi) for the ATP synthase. C) induce a conformational change in the ATP synthase. D) oxidize NADH to NAD+. E) reduce O2 to H2O.
induce a conformational change in the ATP synthase
During oxidative phosphorylation, the proton motive force that is generated by electron transport is used to:
induce a conformational change in the ATP synthase.
The rate of oxidative phosphorylation in mitochondria is controlled primarily by:
the mass-action ratio of the ATD-ADP system.
Mammals produce heat by using the endogenous uncoupling agent:
the protein thermogenin.
Transketolase requires the coenzyme: A) cobalamin (vitamin B12).
thiamine pyrophosphate.
When transketolase acts on fructose 6-phosphate and glyceraldehyde 3-phosphate, the products are:
xyulose 5-phosphate and erythose 4-phosphate
DCMU is an herbicide that acts by blocking photosynthetic electron flow from photosystem II to the cytochrome b6f complex. Predict the effect of DCMU on O2 production and on ATP synthesis in the chloroplasts of plants sensitive to DCMU.
- O2 production would decrease, nowhere for electrons to go - ATP synthesis would decrease because of Cytb6f complex is downstream of the ETC and is the pumper of ATP and doesn't pump effectively - Electrons cycles through the cycle, ATP will decrease but not cease completely - If electrons go to NADPH, then it could be lost - Cyclic is for ATP producing - Non-cyclic is for NADPH - Cyclic is for ATP production without producing NADPH
In normal mitochondria, the rate of NADH consumption (oxidation) will:
-Be increased in active muscle, decreased in inactive muscle. -Be very low if the ATP synthase is inhibited, but increase when an uncoupler is added. -Decrease in mitochondrial ADP is depleted. -Decrease when cyanide is used to prevent electron transfer through the cytochrome a + a3 complex
Refer to the figure. An FoF1 ATP‑dependent active proton transporter consists of a transmembrane proton channel complex, Fo, and a peripheral ATPase complex, F1. ATP hydrolysis causes a conformational change that rotates the 𝛾𝜖 subunit of F1, which in turn rotates the Fo unit and causes protons to be translocated across the membrane. In a mitochondrion, the FoF1 transporter acts as an ATP synthase when there is a sufficiently large proton gradient. Scientists attach a magnetic nanobead to the 𝛾𝜖 subunit of isolated F1. They affix the F1 to the bottom of a microscopic glass chamber such that the bead-F1 𝛾𝜖 portion can freely rotate. First, in a solution containing 500 nM ATP, they observe that the bead-F1 𝛾𝜖 complex spontaneously rotates counterclockwise. These spontaneous rotations stop once the ATP is depleted. Second, in a solution containing 200 nM ATP, 100 μM ADP, and 10 mM Pi, the scientists apply a magnetic field that rotates the bead clockwise. When the magnetic field is switched off, the bead-F1 𝛾𝜖 complex reverts to spontaneous counterclockwise rotations. These spontaneous rotations last longer than those observed in the first experiment starting with 500 nM ATP. Select those statements that explain the results of the experiments using the bead-F1 𝛾𝜖 complex.
-Reversing the direction of the F1 complex's spontaneous rotation results in condensation of ADP and Pi. -The Fo complex is required to drive ATP synthesis by FoF1 transporter in vivo.
molecules through 1 NADH oxidation. 2) Provide at least one reason to rationalize such discrepancy in ATP production. The cell only generates 1.5 ATP molecules through 1 FADH2. 3) Calculate how many protons are pumped through Complex I of the electron transport chain. Show your calculations.
1) Three ATP molecules will be generated as 10 protons pass through 10 c subunits to complete one round of rotation. 2) Some protons can occasionally leak out of the inner mitochondria membrane and reduce the proton gradient, for instance through the uncoupling protein thermogenin. When the electrochemical potential gets high, the proton pumping process might also become less efficient. 3) Four protons are pumped through Complex I. Ten protons can generate 2.5 ATP, so four protons can generate 1 ATP molecule. The major energy efficiency difference between FADH2 and NADH is that Complex I pump protons. Complex I pump 4 protons to account for 1 ATP production difference.
In the carbon assimilation ("dark") reactions of photosynthesis, the biosynthesis of 1 mol of hexose from 6 mol of carbon dioxide requires:
12 mol of NADPH and 18 mol of ATP.
Place the following electron carriers into the proper order as found in plant chloroplasts. 1) Cytochrome b6f complex 2) P680 3) P700 4) Plastocyanin 5) NADPH
2, 1, 4, 3, 5
Place the following electron-carriers into the proper order as found in plant chloroplasts. 1) Cytochrome b6f complex 2) P680 3) P700 4)Plastocyanin 5) NADPH
2, 1, 4, 3, 5
A researcher illuminates a suspension of green algae in the absence of CO2CO2. Then, he incubates the algae with 14CO214CO2 in the dark and observes the conversion of 14CO214CO2 to [14C]glucose for a brief time. What is the significance of this observation with regard to the CO2CO2 assimilation process, and how is it related to the light dependent reactions of photosynthesis? Why does the conversion of 14CO214CO2 to [14C]glucose stop after a brief time?
A. CO2 assimilation requires light generated ATP and NADPH. Once consumption depletes the supply of ATP and NADPH, CO2CO2 assimilation ceases. B. Some enzymes switch off in the dark
In normal mitochondria, the rate of electron transfer is tightly coupled to the demand for ATP. When the rate of ATP use is relatively low, the rate of electron transfer is low; when demand for ATP increases, the electron‑transfer rate increases. Under these conditions of tight coupling, the number of ATP molecules produced per atom of oxygen consumed when NADH is the electron donor (the P/O ratio) is about 2.5. Physicians used to prescribe the uncoupler 2,4‑dinitrophenol (DNP) as a weight‑reducing drug. A. How could this agent, in principle, serve as a weight‑reducing aid? B. Physicians no longer prescribe uncoupling agents, because some deaths occurred following their use. Why might the ingestion of uncouplers cause death?
A. DNP causes increased respiratory chain activity, resulting in increased oxidation of nutrient stores. B. When the P/O approaches zero, the lack of ATP results in death.
When the [NADPH]/[NADP+] ratio in chloroplasts is high, photophosphorylation is predominantly cyclic, as shown. Does cyclic photophosphorylation evolve O2? Does cyclic photophosphorylation produce NADPH? What is the main function of cyclic photophosphorylation?
A. No, because the excited electron from P700 returns to refill the electron "hole" created by illumination. B. No, because the excited electron returns to P700 rather than reducing NADP+. C. to produce ATP
The most prevalent infection in humans worldwide is dental caries, which stems from the colonization and destruction of tooth enamel by a variety of acidifying microorganisms. These organisms synthesize and live within a water insoluble network of dextrans, called dental plaque, composed of (α1→6) linked polymers of glucose with many (α1→3) branch points. Polymerization of dextran requires dietary sucrose, and the bacterial enzyme dextran sucrose glucosyltransferase catalyzes the reaction. Select the overall reaction for dextran polymerization. In addition to providing a substrate for the formation of dental plaque, how does dietary sucrose also provide oral bacteria with an abundant source of metabolic energy?
A. Sucrose+(glucose)𝑛⟶(glucose)𝑛+1+fructose. B. Oral bacteria readily import and metabolize the fructose generated in the synthesis of dextran.
Illuminated green sulfur bacteria carry out photosynthesis in the presence of H2OH2O and CO214CO214, but only if H2SH2S is added and O2O2 is absent. During photosynthesis, measured by formation of [14C] carbohydrate, the bacteria convert H2SH2S to elemental sulfur but do not produce O2.O2. What is the role of the conversion of H2SH2S to sulfur? Why doesn't photosynthesis produce O2O2 in these bacteria?-
A. The bacteria use H2SH2S as a source of protons and electrons.- B. H2OH2O is not split during photosynthesis in these bacteria.
When researchers add O2 to an anaerobic suspension of cells consuming glucose at a high rate, the rate of glucose consumption declines greatly as the cells consume the O2, and accumulation of lactate ceases. This effect, first observed by Louis Pasteur in the 1860s, is characteristic of most cells capable of aerobic and anaerobic glucose catabolism. A. Why does the accumulation of lactate cease after the addition of O2 ? B. Why does the presence of O2 decrease the rate of glucose consumption? C. How does the onset of O2 consumption slow down the rate of glucose consumption?
A. The cell regenerates NAD+ by respiratory electron transfer and oxidative phosphorylation. B. The ATP yield from oxidizing glucose aerobically is much larger than from glycolysis under anaerobic conditions. C. Phosphofructokinase‑1 inhibition slows the rate of glucose entry into glycolysis.
Researchers can produce respiration‑deficient yeast mutants (p−; "petites") from wild‑type parents by treatment with mutagenic agents. The mutants lack cytochrome oxidase, a deficit that markedly affects their metabolic behavior. One striking effect is that fermentation is not suppressed by O2 —that is, the mutants lack the Pasteur effect. Some companies are very interested in using these mutants to ferment wood chips to ethanol for energy use. A. What is the advantage of using these mutants rather than wild‑type yeast for large‑scale ethanol production? B. Why does the absence of cytochrome oxidase eliminate the Pasteur effect?
A. The mutants can produce ethanol in the presence of oxygen, whereas wild‑type yeasts cannot. B. Cells lacking cytochrome oxidase cannot switch from fermentation to aerobic respiration.
In normal mitochondria, the rate of electron transfer is tightly coupled to the demand for ATP. When the rate of ATP use is relatively low, the rate of electron transfer is low; when demand for ATP increases, the electron‑transfer rate increases. Under these conditions of tight coupling, the number of ATP molecules produced per atom of oxygen consumed when NADH is the electron donor (the P/O ratio) is about 2.5. Ingestion of uncouplers causes profuse sweating and an increase in body temperature. A. What causes this phenomenon? B. What happens to the P/O ratio in the presence of uncouplers?
A. The oxidation of additional fuel to produce normal amounts of ATP releases heat, which increases body temperature. B. It approaches zero
Venturicidin is a powerful inhibitor of the chloroplast ATP synthase, interacting with CFo and blocking proton passage through the CFoCF1 complex. How would venturicidin affect oxygen evolution in a suspension of well illuminated chloroplasts? Would your answer change if the experiment were done in the presence of an uncoupling reagent such as 2,4 dinitrophenol (DNP)?
A. When the energy needed to pump protons against the increasing proton gradient is greater than the energy of a photon, oxygen evolution ceases. B. Yes, dissipating the proton gradient restores electron flow and oxygen evolution.
Iodoacetate reacts irreversibly with the free -SH groups of Cys residues in proteins. Which Calvin cycle enzymes would iodoacetate inhibit? Why would iodoacetate inhibit these enzymes?
A. ribulose 5 phosphate kinase, fructose 1,6 bisphosphatase, sedoheptulose 1,7 bisphosphatase, and glyceraldehyde 3 phosphate dehydrogenase. B. Activation of the enzymes depends on the reduction of disulfide bonds between Cys residues to form free -SH groups.
Which of the following is NOT true of the Pi-triose phosphate antiporter?
ATP and reducing equivalents are moved into the chloroplast by the antiporter
Cyclic electron flow in chloroplasts produces:
ATP, but not NADPH or O2
Cyclic electron flow in chloroplasts produces:
ATP, but not NADPH or O2 .
Cyclic electron flow in chloroplasts produces:
ATP, but not NADPH or O2.
A recently discovered bacterium carries out ATP synthesis coupled to the flow of electrons through a chain of carriers to some electron acceptor. The components of its electron transfer chain differ from those found in mitochondria; they are listed below with their standard reduction potentials. A. Predict the flow of electrons with the electron carriers in the right order. B. How would you calculate the maximum number of ATP molecules that could theoretically be synthesized, under standard conditions, per pair of electrons transferred through this chain of carriers? (The Faraday constant, A, is 96.48 kJ/V*mol). Delta G for ATP synthesis is + 30.5 kJ/mol.
Answer to A: - The flow of electrons with the electron carriers are flowing from more negative to positive value because negative value to less negative value (product-reactant) delta G = -negative (spontaneous). Delta E should be positive - FPb (-0.62 V) NAD+ (-0.32 V) CytC (0.22 V) Flavoprotein a (0.77 V) Sulfur Protein (0.89 V) - Transfer of electrons is spontaneous Answer to B: Delta G = -291.4 kJ and ATP produced is 9.71 ATP
Which of these amino acids are converted into oxaloacetate?
Asparagine and Aspartate
In normal mitochondria, the rate of NADH consumption (oxidation) will:
Be increased in active muscle, decreased in inactive muscle. Be very low if the ATP synthase is inhibited, but increase when an uncoupler is added. Decrease if mitochondrial ADP is depleted. decrease when cyanide is used to prevent electron transfer through the cytochrome a + a3 complex.
Photosynthetic phosphorylation and oxidative phosphorylation appear to be generally similar processes, both consisting of ATP synthesis coupled to the transfer of electrons along an electron carrier chain. Which of the following is NOT of both processes?
Both use oxygen as a terminal electron acceptor
Oxidative Phosphorylation and photophosphorylation share all of the following except:
Chlorophyll
Oxidative phosphorylation and photophosphorylation share all of the following EXCEPT:
Chlorophyll
Identify the full biochemical names for each of the complexes in the respiratory chain.
Complex 1- NADH dehydrogenase complex Complex 2- Succinate dehydrogenase complex Complex 3- Cytochrome bc1 complex Complex 4- Cytochrome oxidase
Which of the following is NOT regulated by hypoxia-inducible factor (HIF-1)?
Complex I of the respiratory chain
Which of the following is not regulated by hypoxia-inducible factor (HIF-1)?
Complex I of the respiratory chain
Reduced QH2 is not formed by which of the following?
Complex III and Cytochrome C
Reduced QH2 is not formed by which of the following?
Complex III and cytochrome c
Cyanide, oligomycin, and 2,4-dinitrophenol (DNP) are inhibitors of mitochondrial aerobic phosphorylation. Which of the following statements correctly describes the mode of action of the three inhibitors?
Cyanide inhibits the respiratory chain, whereas oligomycin and 2,4-dinitrophenol inhibit the synthesis of ATP
Cyanide, oligomycin, and 2,4-dinitrophenol (DNP) are inhibitors of mitochondrial aerobic phosphorylation. Which of the following statements correctly describes the mode of action of the three inhibitors?
Cyanide inhibits the respiratory chain, whereas oligomycin and 2,4-dinitrophenol inhibit the synthesis of ATP.
Which one of the following is TRUE about reaction centers?
Cyanobacteria and plants have two reaction centers arranged in tandem
Which of the following is NOT true about cyclic electron flow?
Cyclic electron flow produces more NADPH per photon than noncyclic electron flow
Antimycin A blocks electron transfer between cytochromes b and c1. If intact mitochondria were incubated with antimycin A, excess NADH, and an adequate supply of O2, which of the following would be found in the oxidized state?
Cytochrome a3
In the reoxidation of QH2 by purified ubiquinone-cytochrome c reductase (complex III) from heart muscle, the overall stoichiometry of the reaction requires 2 mol of cytochrome c per mole of QH2 because:
Cytochrome c is one electron acceptor, whereas QH2 is a two-electron donor
Which of these amino acids are converted to alpha-ketoglutarate?
Glutamate, Histidine, Arginine, and Proline
In normal mitochondria, the rate of electron transfer is tightly coupled to the demand for ATP. Under these conditions of tight coupling, the number of ATP molecules produced per atom of oxygen consumed when NADH is the electron donor (the P/O ratio) is about 2.5. Physicians used to prescribe the 2,4-dinitrophenol (DNP) as a weight-reducing agent drug. How could this agent, in principle, serve as a weight-reducing aid?
DNP causes an increased respiratory chain activity, resulting in increased oxidation of nutrient stores
Predict how an inhibitor of electron passage through pheophytin would affect electron flow through photosystem II (PSII) and photosystem I (PSI).-
Electron flow through PSII would stop and electron flow through PSI would slow down.
Given some 14CO214CO2 and all the tools typically present in a biochemistry research lab, how would you design a simple experiment to determine whether a plant is a typical C4 plant or a CAM plant? Complete the passage describing two such experiments.
Experiment 1: Measure the amount of 14CO214CO2 fixed in leaves during an hour of darkness and an hour of bright illumination. The CAM plant will take up much more CO2CO2 at night. Experiment 2: Measure the concentration of organic acids in the vacuoles by titrating an extract of leaves. In darkness, the C4 plant will have a lower level of titratable acidity.
The major regulator of sucrose biosynthesis in plants is:
Fructose-2,6, -bisphosphate
The relative concentrations of ATP and ADP control the cellular rates of:
Glycolysis, oxidative phosphorylation, pyruvate oxidation, and the citric acid cycle
In 1804, Theodore de Saussure observed that the total weight of oxygen and dry organic matter produced by plants is greater than the weight of carbon dioxide consumed during photosynthesis. Where does the extra weight come from?-
H2O
The light absorbing pigments in the thylakoid membranes of chloroplasts are organized into two photosystems: photosytem II (PSII) and photosytem I (PSI). Using a spectrophotometer, researchers can sometimes directly observe the extent of oxidation or reduction of an electron carrier during photosynthetic electron transfer. Illuminating chloroplasts with 700 nm700 nm light oxidizes cytochrome f, plastocyanin, and plastoquinone. Illuminating chloroplasts with 680 nm680 nm light, however, reduces these electron carriers. Complete the passage explaining this observation.
Illuminating chloroplasts with 700 nm700 nm light excites PSI, but not PSII. The P700 reaction center donates electrons to NADP+, but no electrons flow from P680 to replace them. Illuminating chloroplasts with 680 nm680 nm light excites PSII, but not PSI. Electrons tend to flow to PSI, but the electron carriers between the two photosystems quickly become completely reduced.
Researchers illuminate a maize (corn) plant in the presence of 14CO2.14CO2. After about 1 second of illumination, they find more than 90% of all the radioactivity incorporated in the leaves at C 4 of malate, aspartate, and oxaloacetate. Only after 60 seconds does 14C14C appear at C 1 of 3 phosphoglycerate. Complete the passage explaining these findings.
In maize, the C4 pathway fixes CO2.CO2. Phosphoenolpyruvate (PEP) carboxylase carboxylates PEP to form oxaloacetate. Some of this product undergoes transamination to aspartate, but most undergoes reduction to malate in the mesophyll cells. Only after subsequent decarboxylation of labeled malate does 14CO214CO2 enter the Calvin cycle for conversion to glucose. The rate of the rubisco catalyzed reaction, which incorporates the labeled CO2CO2 at the C 1 position of 3 phosphoglycerate, limits the rate of 14CO214CO2 entry into the Calvin cycle.
Which of the following is NOT a feature of complex IV?
In order to generate two water molecules, complex IV must go through the catalytic cycle two times (4 times)
Which of the following is not a feature of complex IV?
In order to generate two water molecules, complex IV must go through the catalytic cycle two times.
n‑Butylmalonate inhibits the transport system that conveys malate and α‑ketoglutarate across the inner mitochondrial membrane. Suppose you add n‑butylmalonate to an aerobic suspension of kidney cells using glucose exclusively as fuel. Predict the effect of this inhibitor on glycolysis, oxygen consumption, lactate production, and ATP synthesis.
In the presence of n‑butylmalonate, glycolysis operates anaerobically, oxygen consumption decreases, lactate production increases, and ATP synthesis decreases.
During oxidative phosphorylation, the proton motive force that is generated by electron transport is used to:
Induce a conformational change in ATP synthase
What role does superoxide dismutase play in ameliorating the effects of reactive oxygen species?
It catalyzes the conversion of superoxide to hydrogen peroxide and O2.
In what order do the following five steps occur in the photochemical reaction centers?
Light excitation of antenna chlorophyll molecule, Excitation transfer to neighboring chlorophyll, Excitation of the chlorophyll a molecule at the reaction center, Passage of excited electron to electron-transfer chain, and Replacement of the electron in the reaction center chlorophyll
Which of the following is NOT found in modern cyanobacteria?
Mitochondria
Mutations in the genes that encode certain mitochondrial proteins are associated with a high incidence of some types of cancer. How might defective mitochondria lead to cancer?
Mitochondrial defects can lead to increased production of reactive oxygen species. These species can react with nuclear DNA and convert proto‑oncogenes to oncogenes.
The glycine decarboxylase complex in the leaves of pea or spinach plants are mainly localized in the:
Mitochondrion
The subcellular organelles involved in the phosphoglycolate salvage pathway are:
Mitochondrion, peroxisome, and chloroplast
The three subcellular organelles involved in the phosphoglycolate salvage pathway are: A) endoplasmic reticulum, chloroplast, and mitochondrion. B) nucleus, endoplasmic reticulum, and chloroplast. C) golgi apparatus, chloroplast, and mitochondrion. D) mitochondrion, peroxisome, and chloroplast. E) peroxisome, endoplasmic reticulum, and chloroplast.
Mitochondrion, peroxisome, and chloroplast
Under aerobic conditions, extramitochondrial NADH must undergo oxidation by the mitochondrial respiratory chain. Consider a preparation of rat hepatocytes containing mitochondria and all the cytosolic enzymes. After the introduction of [4‑H3] NADH, radioactivity soon appears in the mitochondrial matrix. Conversely, no radioactivity appears in the matrix after the introduction of [7‑C14] NADH. What do these observations reveal about the oxidation of extramitochondrial NADH by the respiratory chain?
NAD+ and NADH cannot directly pass through the inner membrane, thus the labeled NAD moiety of [7‑14C] NADH remains in the cytosol. The 3H on [4‑3H] NADH enters the mitochondria via the malate‑aspartate shuttle.
Compound X is an inhibitor of mitochondrial ATP synthesis. It was observed that when compound X was added to cells, the NAD+/NADH ratio decreased. Would you expect X to be an uncoupling agent or an inhibitor of respiratory electron transfer? Explain.
NADH (blocked by Rotenone) Q Cyt b Cyt C1 Cyt C Cyt (a + a3) O2 NADH Q Cyt b (blocked by Antimycin A) Cyt C1 Cyt C Cyt (a + a3) O2 NADH Q Cyt b Cyt C1 Cyt C Cyt (a + a3) (blocked by CN- or CO) O2 - Uncoupling agents are small molecules that interrupt membrane potential on membrane - Inhibitor inhibits the electron transfer - Inhibits electrons because ratio changed and electrons stay in NADH, the electron never gets transferred and accumulate. You're not producing NAD+ - If you add an uncoupling agent, ATP won't be synthesized, electrons aren't affected
Isolated spinach chloroplasts evolve O2 when illuminated in the presence of potassium ferricyanide (a Hill reagent), according to the equation: 2H2O + 4Fe3+ ----> O2 + 4H + 4Fe2+ where Fe3+ represents ferricyanide and Fe 2+, ferrocyanide. Does this process produce NADPH?
No, ferricyanide removes electrons from the photosynthetic system, leaving non-available for NADP+ reduction
Isolated spinach chloroplasts evolve O2O2 when illuminated in the presence of potassium ferricyanide (a Hill reagent), according to the equation 2H2O+4Fe3+⟶O2+4H++4Fe2+2H2O+4Fe3+⟶O2+4H++4Fe2+ where Fe3+Fe3+ represents ferricyanide and Fe2+,Fe2+, ferrocyanide. Does this process produce NADPH? -
No, ferricyanide removes electrons from the photosynthetic system, leaving none available for NADP+ reduction.
In "C4" plants of tropical region origin, the first intermediate into which 14CO2 is fixed is:
Oxaloacetate
Place the following electron carriers into the proper order found in plant chloroplasts.
P680, Cytochrome b6f complex, Plastocyanin, P700, NADPH
Which of these enzymes is NOT part of the Calvin Cycle?
Phosphofructokinase-1
Which of these enzymes is not part of the Calvin cycle?
Phosphofructokinase-1
The known mechanism of activation of rubisco or of other enzymes of the Calvin Cycle during illumination include all of the following EXCEPT:
Phosphorylation by cAMP-dependent protein kinase
How can the chloroplast overcome this unfavorable equilibrium?-
The absorption of photons provides the energy needed for the chloroplasts to overcome this barrier.
When researchers add O2 to an anaerobic suspension of cells consuming glucose at a high rate, the rate of glucose consumption declines greatly as the cells consume the O2, and accumulation of lactate ceases. This effect, first observed by Louis Pasteur in the 1860s, is the characteristic of most cells capable of aerobic and anaerobic glucose catabolism. Why does the accumulation of lactate cease after the addition of O2?
The cell regenerates NAD+ by respiratory electron transfer and oxidation phosphorylation
In an organism (such as E. coli) that has both the citric acid cycle and the glyoxylate cycle, what determines which of these pathways isocitrate will enter?
The enzyme metabolizing isocitrate in each pathway is under reciprocal allosteric regulation.
Malic enzyme, found in the bundle sheath cells of C4 plants, carries out a reaction that has a counterpart in the citric acid cycle. What is the analogous reaction in the citric acid cycle?
The isocitrate dehydrogenase reaction
Malic enzyme, found in the bundle-sheath cells of C4 plants, carries out a reaction that has a counterpart in the citric acid cycle. What is the analogous reaction in the citric acid cycle?
The isocitrate dehydrogenase reaction
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. Why?
The mitochondria and cytosol contain separate pools of NAD.
Researchers can produce respiration-deficient yeast mutants (p-; "petites") from wild-type parents by treatment with mutagenic agents. The mutants lack cytochrome oxidase, a deficit that markedly affects their metabolic behavior. One striking effect is that fermentation is not suppressed by O2-- that is, the mutants lack the Pasteur effect. Some companies are very interested in using these mutants to ferment wood chips to ethanol for energy use. What is the advantage of using these mutants rather than wild-type yeast for large-scale ethanol production?
The mutants can produce ethanol in the presence of oxygen in completely aerobic environments
Transketolase requires the coenzyme:
Thiamine pyrophosphate
The precursors for sucrose biosynthesis are:
UDP-glucose and fructose-6-phosphate
Compare the likely time scales for the adjustments in respiratory rate caused by increased [ADP] and reduced 𝑝O2. What accounts for the difference?
Under conditions of increased [ADP], the resulting increase in respiratory rate is limited by the rate of diffusion of ADP. Thus, the response occurs in fractions of a millisecond. Under conditions of decreased pO2, the adjustment to hypoxia requires a change in the concentration of several proteins. The time scale for protein synthesis and degradation is typically seconds to hours.
Which of the following is correct concerning the mitochondrial ATP synthase?
When it catalyzes the ATP synthesis reaction, the delta G is actually close to zero
Venturicidin is a powerful inhibitor of the chloroplast ATP synthase, interacting with CF0 and blocking proton passage through CF0CF1 complex
When the energy needed to pump protons against the increasing proton gradient is greater than the energy of a photon, oxygen evolution ceases
In normal mitochondria, the rate of NADH consumption (oxidation) will:
all of the above
The relative concentrations of ATP and ADP control the cellular rates of:
all of the above
For mutant yeast strain in question 1, why does the absence of cytochrome oxidase eliminate the Pasteur effect?
cells lacking cytochrome oxidase cannot switch from fermentation to aerobic respiration
Reduced QH2 is not formed by which of the following? A) Complex I and NADH B) Complex II and succinate C) Complex III and cytochrome c D) Fatty acid oxidation E) Oxidation of glycerol-3-phosphate
complex III and cytochrome c
Which of these enzymes is NOT part of the calvin cycle?
phosphofructokinase-1
The oxidation of a particular hydroxy substrate to a keto product by mitochondria has a P/O ratio of less than 2. The initial oxidation step is very likely directly coupled to the:
reduction of a flavoprotein.
The light reactions in photosynthetic higher plants:
result in the splitting of H2O, yielding O2.