Biochemistry CH 18
What evidence demonstrated the ATP synthase has components that can actually rotate?
33 subunits were cloned and expressed with the subunits bearing a poly-histidine tag which binds nickel ions. This allowed the F1 subunit to be attached to a nickel coated slide. Using fluorescently tagged actin linked to the subunit, the ATP dependent rotation could be observed using a fluorescent microscope.
In the Rieske center, the iron-sulfur center is coordinated to the amino acid(s) _______. A) His B) Cys C) His and Cys D) Cys and Met E) None of the answers is correct.
A) His
Choose the correct path taken by a pair of electrons as it travels down the electron-transport chain. A) NADH Complex I CoQ Complex III Cyt c Complex IV O2 B) FADH2 Complex I CoQ Complex III Cyt c Complex IV O2 C) NADH Complex I Complex II Complex III Cyt c Complex IV O2 D) FADH2 Complex III CoQ Complex II Cyt c Complex IV O2 E) None of the answers is correct.
A) NADH Complex I CoQ Complex III Cyt c Complex IV O2
What is a cytochrome? A) a protein that transfers electrons and that also contains a heme prosthetic group B) a chloroplast protein that transfers electrons and that also contains an iron sulfur prosthetic group C) a protein that pumps ATP and that also contains iron D) an enzyme that reduces oxygen to water E) None of the answers is correct.
A) a protein that transfers electrons and that also contains a heme prosthetic group
What name is given to the hypothesis proposed by Peter Mitchell that explains how ATP synthesis is coupled to electron transport? A) chemiosmotic hypothesis B) oxidative phosphorylation hypothesis C) electron transport hypothesis D) proton-motive force hypothesis E) None of the answers is correct.
A) chemiosmotic hypothesis
Which of the following does NOT participate in, nor is a component of, the electrontransport chain? A) lipoic acid B) nonheme, iron-sulfur proteins C) FADH2 D) cytochrome c1 E) NADH
A) lipoic acid
What organelle is the site of oxidative phosphorylation in eukaryotes? A) mitochondria B) chloroplast C) lysosome D) endoplasmic reticulum E) Golgi apparatus
A) mitochondria
In the malate-aspartate shuttle, electrons from NADH are transferred to ________, forming malate. A) oxaloacetate B) aspartate C) acetate D) glutamate E) None of the answers is correct.
A) oxaloacetate
Electron flow down the electron-transport chain leads to the A) transport of protons across the inner mitochondrial membrane from inside the matrix to the intermembrane space. B) transport of protons across the inner mitochondrial membrane from the intermembrane space into the matrix. C) coupled synthesis of GTP. D) a dangerous imbalance of K+ ions across the mitochondrial membrane. E) None of the answers is correct.
A) transport of protons across the inner mitochondrial membrane from inside the matrix to the intermembrane space.
What is the net ATP obtained from one cytoplasmic NADH when it is reoxidized by the electron-transport chain using the glycerol 3-phosphate shuttle? A) 2.5 B) 1.5 C) 2.0 D) 1.0 E) None of the answers is correct.
B) 1.5
When glucose is totally oxidized to CO2 and H2O and the glycerol 3-phosphate shuttle is used, how many ATP molecules are made by oxidative phosphorylation (nonsubstrate-level phosphorylation) relative to the maximum yield? A) 12 out of 30 B) 26 out of 30 C) 26 out of 32 D) 12 out of 32 E) None of the answers is correct.
B) 26 out of 30
What is the reaction of ATP synthase? A) AMP3- + 2 HPO42- + H+ ATP4- + H2O B) ADP3- + HPO42-+ H+ ATP4-+ H2O C) ADP3- + HPO42- + 2 H+ ATP4- + H2O D) AMP3- + 2 HPO42- + 2 H+ ATP4- + H2O E) None of the answers is correct.
B) ADP3- + HPO42-+ H+ ATP4-+ H2O
Which of the following does not pump protons? A) Complex I B) Complex II C) Complex III D) Complex IV E) All of the answers are correct.
B) Complex II
Which enzyme catalyzes the reduction of oxygen to water? A) ATP synthase B) cytochrome c oxidase C) NADH-Q oxidoreductase D) Q-cytochrome c oxidoreductase E) succinate-Q reductase
B) cytochrome c oxidase
What term is used to describe an ATP-generating process in which an inorganic substance such as oxygen serves as the ultimate electron acceptor? A) electron transport B) respiration C) fermentation D) anaerobic phosphorylation E) None of the answers is correct.
B) respiration
What is the chemical effect of oligomycin on aerobic metabolism? A) The flow of electrons from NADH to CoQ is blocked. B) The flow of electrons from Cyt a-a3 to oxygen is blocked. C) Oligomycin blocks the proton transfer through F0 of ATP synthase and therefore blocks the phosphorylation of ADP to form ATP. D) The transport of ATP out of and ADP into the mitochondria is blocked. E) Oxidative phosphorylation is uncoupled from electron transport and all the energy is lost as heat.
C) Oligomycin blocks the proton transfer through F0 of ATP synthase and therefore blocks the phosphorylation of ADP to form ATP.
What type of enzyme plays a key role in apoptosis? A) cytochrome P450 B) electron-transport complexes C) caspase D) enzymes of the citric acid cycle E) None of the answers is correct.
C) caspase
Which electron carrier has an isoprenoid tail? A) NADH B) cytochrome c C) coenzyme Q D) FADH2 E) None of the answers is correct.
C) coenzyme Q
What type of gradient is critical to ATP formation by oxidative phosphorylation? A) sodium ion B) chloride ion C) proton D) potassium ion E) None of the answers is correct.
C) proton
Which of the citric acid cycle enzymes is also part of an electron-transport complex? A) isocitrate dehydrogenase B) -ketoglutarate dehydrogenase C) succinate dehydrogenase D) malate dehydrogenase E) None of the answers is correct.
C) succinate dehydrogenase
In prokaryotes the site of ATP-synthesizing machinery is A) the mitochondrial matrix. B) the outer cell wall. C) the cytoplasmic membrane. D) the nucleolus. E) None of the answers is correct.
C) the cytoplasmic membrane.
Explain why carbon monoxide is toxic.
Carbon monoxide binds to the ferrous ion of cytochrome a3 of cytochrome c oxidase. This blocks the electron flow to oxygen and the proton-motive force can no longer be generated. Without the proton gradient, the phosphorylation of ADP ceases.
Explain why less ATP is made from the reoxidation of FADH2 as compared to NADH.
Complex II is not a proton pump. When electrons flow from FADH2 to oxygen, as catalyzed by Complex II, Complex III, and Complex IV, fewer protons are pumped out of the matrix as compared to NADH. Thus, fewer ATP molecules are ultimately made.
Discuss the evolution of the cytochrome c protein.
Cytochrome c has been studied in many organisms with mitochondrial respiratory systems and shows little divergence. Cytochrome c, from many different organisms, can react with the cytochrome c oxidase from other organisms, demonstrating little structural difference at their interfaces. The amino acid sequences of the various cytochrome c proteins are similar and, over a billion years of evolution, 25% of the amino acids remained unchanged.
What type of protein makes the outer mitochondrial membrane relatively permeable? A) proton pump B) voltage gated transporter C) ATP-powered pump D) porin E) None of the answers is correct.
D) Porin
Which enzyme transfers electrons from a membrane-soluble carrier to a water-solublecarrier in the electron-transport process? A) ATP synthase B) cytochrome c oxidase C) NADH-Q oxidoreductase D) Q-cytochrome c oxidoreductase E) succinate-Q reductase
D) Q-cytochrome c oxidoreductase
The energy for ATP synthesis is generated by the movement of protons from the ______________ side of the inner mitochondrial membrane establishing a(an) _____________gradient. A) intermembrane; pH B) intermembrane; electrical potential C) matrix; sodium ion D) matrix; pH E) None of the answers is correct.
D) matrix; pH
What process allows cytoplasmic NADH to be reoxidized by O2 using the electrontransport system? A) glycerol 3-phosphate shuttle B) cytochrome c shuttle C) malate-aspartate shuttle D) quinone shuttle E) glycerol 3-phosphate shuttle and malate-aspartate shuttle
E) glycerol 3-phosphate shuttle and malate-aspartate shuttle
What prosthetic group is present in complexes I, II, and III of electron transport? A) semiquinone B) flavin mononucleotide C) coenzyme Q D) heme group E) iron-sulfur cluster
E) iron-sulfur cluster
How does the glycerol 3-phosphate shuttle function?
Electrons from NADH are transferred to DHAP, to form glycerol-3-P, a reaction that occurs in the cytosol. Glycerol-3-P diffuses through the outer membrane and then transfers the electrons to FAD in a reaction catalyzed by glycerol-3-phosphate dehydrogenase located in the inner membrane. The FADH2 then transfers the electrons to Q.
What is the currently accepted model which explains the presence of mitochondria in eukaryotic cells? What is the best evidence which supports this model?
It is believed that the organelles are the result of a single endosymbiotic event in which one cell engulfed a bacterium. The structure of mitochondria is consistent with this theory in that it has the general size and physical characteristics of a bacterium including a double membrane and a circular (or sometimes linear) genome. Furthermore, DNA sequence analysis suggests that an ancestor of an existing bacterium is the source for extant mitochondria.
Provide a brief description of oxidative phosphorylation.
It is the process in which ATP is formed, due to the transfer of electrons from NADH or FADH2 to O2 by a series of electron carriers in the inner membrane of the mitochondria.
What is the driving force for electron transport through the electron-transport chain?
NADH is a strong reducing agent and is poised to donate electrons to a strong oxidizing agent such as O2. Transfer of two electrons from NADH to O2 results in a substantial release of free energy (-220.1 kJ mol-1).
In the malate-aspartate shuttle, how is oxaloacetate regenerated since there is no transporter for oxaloacetate across the inner membrane?
Oxaloacetate is interconverted between malate and α-ketoglutarate, which requires the concomitant interconversion of glutamate and aspartate. Identical sets of reactions take place both inside and outside the mitochondria to accomplish the translocation of NADH reducing equivalents.
Give the balanced equation for the net reaction catalyzed by Q-cytochrome c oxidoreducatase.
QH2 + 2 Cyt cox + 2 H+ matrix Q + 2 Cyt cred + 4 H+ cytosol
Describe the function of protons in the mechanism of ATP synthesis by the F1 subunit of ATP synthase.
Recent evidence suggests that the role of the proton gradient is not to form ATP but to release it from the synthase. The proton gradient is necessary for ATP synthesis because the binding of a proton to the enzyme causes a conformational change that releases the bound ATP.
Draw the structure of a mitochondrion and indicate the sites of oxidative phosphorylation and the citric acid cycle. Be sure to label your figure to clearly denote where these processes take place.
The drawing should include the overall shape with the outer membrane and the inner membrane, the inner-membrane space, matrix, and cristae labeled. Most of the TCA cycle takes place in the matrix, while oxidative phosphorylation occurs in the inner mitochondrial membrane. It should closely resemble text Figure 18.2.
How is oxidative phosphorylation regulated?
The electrons do not flow unless ADP is available to be simultaneously phosphorylated to ATP. Thus, the synthesis of ATP does not occur unless ADP levels are high. This is referred to as acceptor control.
Describe the major defensive strategy that cells employ to prevent the harmful effects of the reactive oxygen species (ROS) that are inevitably produced during respiration.
The enzyme superoxide dismutase converts superoxide radicals to peroxide and oxygen (requires protons), and the enzyme catalase converts hydrogen peroxide to water and oxygen. Both of these enzymes are ubiquitously expressed and operate at near perfect catalytic efficiency.
What are uncoupling agents? Provide an example of when these might be useful.
Uncoupling agents destroy the proton gradient across the inner membrane by carrying protons back into the matrix. This disrupts the coupling of electron transport to oxidative phosphorylation, and the energy is released as heat instead of being used to drive phosphorylation of ADP. Brown fat utilizes an uncoupling agent UCP-1 as a means of accomplishing non-shivering thermogenesis to generate heat for newborns. Other examples of the function of brown fat are also acceptable examples.
