Exam 3 Smartwork Questions
When NADH or NADPH transfers electrons to a recipient molecule, the recipient becomes reduced and the activated carriers are oxidized (to NAD+ or NADP+, respectively). What else happens during this reaction? Choose one: A. A proton is taken up by the recipient molecule. B. A proton is released into the solution. C. A phosphate group is transferred to the recipient molecule. D. A proton is taken up by the carrier. E. A molecule of water is released into the solution.
A. A proton is taken up by the recipient molecule.
Which statement about enzymes is not true? Choose one: A. An enzyme can force an energetically unfavorable reaction to take place inside the cell. B. Enzymes can help build large polymers. C. Enzymes reduce the activation energy required to initiate a spontaneous reaction. D. Enzymes can speed up energetically favorable reactions.
A. An enzyme can force an energetically unfavorable reaction to take place inside the cell.
Antibiotics should inhibit bacterial cell growth without generating side effects in the human patient, but that is not always the case. Some antibiotics that inhibit bacterial protein synthesis by binding to bacterial ribosomes induce negative side effects in patients. What is the most likely cause of these side effects? Choose one: A. The antibiotics interfere with mitochondrial ribosomes. B. The antibiotics interfere with cytoplasmic ribosomes. C. The antibiotics interfere with ribosomes attached to the ER, impairing RER function. D. The antibiotics interfere with chloroplast ribosomes.
A. The antibiotics interfere with mitochondrial ribosomes.
Which statement is true? Choose one: A. The heat released by an animal cell comes from the chemical bond energy present in the food molecules it metabolizes. B. A cell takes in heat from the environment to power its biosynthetic reactions, thereby obeying the second law of thermodynamics. C. Cells obey the first law of thermodynamics but are exempt from the second law. D. The breakdown of food molecules generates heat, which cells then use to drive the synthesis of large molecules. E. A cell generates order by decreasing the entropy of its surroundings.
A. The heat released by an animal cell comes from the chemical bond energy present in the food molecules it metabolizes.
In a cell, the rate at which an enzyme will encounter its substrate depends on which of the following? Choose one: A. the concentration of the substrate B. the way that the cytosol is structured C. the concentration of other proteins in the cytosol D. the size of the enzyme
A. the concentration of the substrate
What provides the fuel to convert CO2 into sugars in chloroplasts?Choose one: ATP generated by cell respiration oxidation of food molecules Nothing; the reactions do not require energy. ATP and NADPH generated in the photosynthetic light reactions a proton gradient across a membrane
ATP and NADPH generated in the photosynthetic light reactions
The ΔG° of the hydrolysis reaction of ATP is -7.3 kcal/mole, but in a cell the actual ΔG is much more negative. What is the reason for the ΔG° and ΔG difference? Choose one: A. The concentration of ATP is much lower than the concentrations of its hydrolysis products, ADP and Pi. B. ATP is much higher in concentration than the products ADP and Pi .C. Cells use enzymes to perform these reactions, resulting in a difference between ΔG° and ΔG .D. None of the above address the ΔG° and the cellular ΔG difference.
B. ATP is much higher in concentration than the products ADP and Pi
Which of the following statements regarding NADPH and NADH is true? Choose one: A. NADPH and NADH deliver electrons to the same set of enzymes. B. NADPH and NADH are used in separate biochemical pathways in cells. C. NADPH loses a phosphate group to form NADH during biosynthetic reactions. D. NADH carries electrons in animal cells and NADPH does the same in plants.
B. NADPH and NADH are used in separate biochemical pathways in cells.
How do the high-energy electrons of activated carriers contribute to forming the high-energy phosphate bonds of ATP? Choose one: A. They are transferred directly to ADP to form ATP. B. They are used by the electron-transport chain to make a proton gradient. C. They are passed to ATP synthase to power ATP synthesis. D. They are pumped across the membrane to form an electron gradient.
B. They are used by the electron-transport chain to make a proton gradient.
What is the role of activated carriers in cells? Choose one: A. They carry energy from anabolic reactions for use in catabolic reactions. B. They capture energy from energy releasing reactions and transfer it to other reactions. C. They are enzymes that catalyze the reactions that break down foodstuffs for energy generation in the cell. D. They are enzymes that catalyze biosynthetic reactions and make them feasible at the temperature of a cell.
B. They capture energy from energy releasing reactions and transfer it to other reactions.
Consider two molecules that associate with each other through hydrogen bonds. How tightly will the two molecules bind as the equilibrium constant, K, becomes larger for this association? Choose one: A. The equilibrium constant will have no bearing on how tightly they bind. B. They will bind more tightly. C. They will bind less tightly.
B. They will bind more tightly.
Your company has developed an organic molecule with commercial potential and you know how to produce it in the lab. You want to increase production and make as much of the molecule as possible, but the reaction has a positive ΔG°. What can you do to try to drive the reaction toward your desired product? Choose one or more: A.add an enzyme that does not couple to another reaction B.continually remove products C.increase the concentration of reactants D.add some products initially to get the reaction primed
B.continually remove products C.increase the concentration of reactants
Which is not true of a chemical reaction at equilibrium? Choose one: Both the forward and reverse reactions have stopped. The net concentrations of substrate and product do not change. ΔG is equal to zero. The rates of the forward and reverse reactions are equal.
Both the forward and reverse reactions have stopped.
Which of the following statements is not true? Choose one: A. When a sugar molecule is oxidized to CO2 and H2O, the O2 molecules involved in forming the H2O are reduced. B. Oxidation and reduction reactions always occur simultaneously. C. Hydrogenation reactions are oxidations, and dehydrogenation reactions are reductions. D. When a carbon atom in a C-H bond has somewhat more than its share of electrons, it is said to be reduced.
C. Hydrogenation reactions are oxidations, and dehydrogenation reactions are reductions.
What is true of the evolution of electron transport systems? Choose one: A. In ancient prokaryotes, they did not require the use of a membrane. B. Their requirement for oxygen as an electron acceptor means they evolved first in photosynthetic prokaryotes. C. They are evolutionarily ancient and likely provided energy for the earliest cells on Earth. D. They are a relatively recent evolutionary innovation. E. The earliest ones involved using H2O as an electron donor.
C. They are evolutionarily ancient and likely provided energy for the earliest cells on Earth.
What is the function of a kinase? Choose one: A. to rearrange the bonds into an isomeric form B. to oxidize a molecule C. to add a phosphate group to a molecule D. to shift a chemical group from one position to another in a molecule
C. to add a phosphate group to a molecule
Carbon atoms cycle continuously through the biosphere. What is a by-product of cell respiration, and what does this by-product represent? Choose one: C6H12O6; completely oxidized carbon CO2; a reduced version of carbon C6H12O6; a reduced version of carbon CO2; completely oxidized carbon
CO2; completely oxidized carbon
Cytochrome c oxidase catalyzes the reaction that reduces molecular oxygen (two oxygen atoms) to two water molecules. The electrons are added sequentially, and during the process cytochrome c oxidase must bind the oxygen tightly in the active site. Why? Choose one: A. If the oxygen escapes, it will bubble out as a gas and escape quickly. B. Oxygen will bind to the electron-transport chain and reverse the pumping of protons. C. The escaped oxygen will form carbon monoxide and kill the cell. D. Superoxide radicals are formed as an intermediate, and are dangerous to the cell.
D. Superoxide radicals are formed as an intermediate, and are dangerous to the cell.
For a reaction Y → X with a very high equilibrium constant, K, which of the following is true? You can refer to the following two equations in formulating your answer. K=[X]/[Y] ΔG=ΔG°+RT In([X]/[Y]) A. The amount of product and substrate are equal at equilibrium. B. The forward reaction rate greatly exceeds the reverse reaction rate at equilibrium. C. The standard free-energy change is large and positive. D. The amount of product will be higher than the amount of substrate at equilibrium.
D. The amount of product will be higher than the amount of substrate at equilibrium.
Your friends are on a low-fat, high-carbohydrate diet, which they claim will prevent fat accumulation within their bodies. They eat tons of pasta and bread without worrying about calorie count. What can you correctly say to your friends about their potential to accumulate lipids on their low-fat diet? Choose one: A. They will not accumulate fats because carbohydrates have less energy per gram than fats. B. They will not accumulate fats because cells have no way of storing fats. C. They will accumulate fats because cells have no way of storing carbohydrates. D. They will accumulate fats because cells can convert glycolytic metabolites into lipids.
D. They will accumulate fats because cells can convert glycolytic metabolites into lipids.
The energies of phosphate bonds for different molecules in glycolysis are shown. Based on this graphic, the transfer of a phosphate from which of the molecules to ADP (to form ATP) is energetically UNFAVORABLE? Choose one: A. They are all energetically favorable. B. phosphoenolpyruvate C. 1,3-bisphosphoglycerate D. glucose 6-phosphate
D. glucose 6-phosphate
What is the origin of the energy that animals acquire by eating plants or other animals? Choose one: A. heat B. carbohydrates C. sugars D. sunlight E. fats
D. sunlight
Which of the following does not describe an oxidation reaction?Choose one: A. the conversion of Fe2+ to Fe3+ B. the addition of oxygen atoms to a molecule C. the removal of electrons from a molecule D. the conversion of a chlorine atom to Cl-
D. the conversion of a chlorine atom to Cl-
Which is true about electrons as they move through the electron-transport chain? Choose one: A. Electrons start out at very low energy and gain energy at each transfer step. B. Electrons are pumped across the mitochondrial membrane as they move along the electron-transport chain. C. Electrons neither gain nor lose energy as they move along the electron-transport chain. D. Electrons can gain or lose energy, depending on where they enter along the electron-transport chain. E. Electrons start out at very high energy and lose energy at each transfer step along the electron-transport chain.
E. Electrons start out at very high energy and lose energy at each transfer step along the electron-transport chain.
In thermodynamics, what does the term "free energy" refer to? Choose one: A. energy that cannot be harnessed to do work or drive chemical reactions B. energy that cells borrow from the environment C. excess energy from a reaction that a cell does not use D. energy required to initiate a chemical reaction E. energy that can be harnessed to do work or drive chemical reactions
E. energy that can be harnessed to do work or drive chemical reactions
Chemical reactions proceed spontaneously only in which direction?Choose one: A. one that leads to an increase in orderliness B. one that goes "uphill" C. one that is energetically unfavorable D. one that releases water E. one that leads to a release of free energy
E. one that leads to a release of free energy
Ubiquinone has a redox potential of +30 mV, while cytochrome c has a redox potential of +230 mV. During electron transport, which is true? Choose one: Electrons will flow from ubiquinone to cytochrome c. Electrons will move back and forth between ubiquinone and cytochrome c. The direction of electron flow will depend on the ATP/ADP ratio. Electrons will not flow in either direction. Electrons will flow from cytochrome c to ubiquinone.
Electrons will flow from ubiquinone to cytochrome c.
When ATP and food molecules such as fatty acids are abundant, which will occur? Choose one: When food molecules are plentiful, neither glycolysis nor gluconeogenesis will occur. Enzymes involved in gluconeogenesis will use energy to produce glucose. Enzymes involved in glycolysis will operate in the reverse direction, using pyruvate to produce glucose. Enzymes involved in glycolysis will break down glucose to generate pyruvate. When food and ATP are plentiful, both glycolysis and gluconeogenesis will occur.
Enzymes involved in gluconeogenesis will use energy to produce glucose.
C. Forward reaction A would increase.
For the following uncatalyzed reaction at equilibrium, how would the reaction change if it was now an enzyme-catalyzed reaction at equilibrium? Choose one: A. Reverse reaction B would decrease. B. Levels of Y would increase. C. Forward reaction A would increase. D. Levels of X would increase.
What is true of the phosphorylation of glucose in step 1 of glycolysis? Choose one: It is carried out by an enzyme called phosphoglucokinase. It is energetically unfavorable. It produces NADH. It traps the sugar inside the cell. It has a ΔG° of 8 kcal/mole.
It traps the sugar inside the cell.
What happens to the ATP produced during stage 1 of photosynthesis? Choose one: It is exported from the chloroplast to fuel the plant's metabolic needs. It is exported from the chloroplast and used to produce sucrose. It is consumed within the chloroplast to produce NADPH. It is consumed within the chloroplast to produce glyceraldehyde 3-phosphate. It is consumed within the chloroplast to fuel electron transport.
It is consumed within the chloroplast to produce glyceraldehyde 3-phosphate.
When the difference in redox potential between two molecules is highly positive, what is true of the transfer of electrons between them? Choose one: It produces ATP. It is highly favorable. It is accompanied by a rise in ΔG. It is highly unfavorable. It requires an input of energy.
It is highly favorable.
Which statement is true of glycogen phosphorylase? Choose one: It is inhibited by glucose 6-phosphate and by ATP. It is activated by glucose 6-phosphate and by ATP. It is inhibited by glucose 6-phosphate, but activated by ATP. It is activated by glucose 6-phosphate, but inhibited by ATP. It stimulates gluconeogenesis.
It is inhibited by glucose 6-phosphate and by ATP.
What happens to the energy captured during glycolysis and the citric acid cycle by the activated carriers NADH and FADH2. Choose one: It is passed to ADP to form ATP. It is used to drive biosynthetic reactions. It is passed to an electron transport chain that uses it to produce oxygen. It is passed to an electron transport chain that uses it to generate a proton gradient across the inner mitochondrial membrane. It is passed to an electron transport chain that uses it to oxidize food molecules.
It is passed to an electron transport chain that uses it to generate a proton gradient across the inner mitochondrial membrane.
Although the citric acid cycle itself does not use O2, it requires a functioning electron transport chain (which uses O2) in order to regenerate which molecule for further use in the citric acid cycle?Choose one: ATP NADH FADH2 ADP NAD+
NAD+
What are the end products of glycolysis? Choose one or more: NADH ADP ATP NADPH H2O + CO2 acetyl CoA pyruvate
NADH ATP pyruvate
In the electron-transport chain in chloroplasts, which molecule serves as the final electron acceptor? Choose one: O2 H2O ADP NADP+ NAD+
NADP+
Investigators introduce two proteins into the membrane of artificial lipid vesicles: (1) an ATP synthase isolated from the mitochondria of cow heart muscle, and (2) a light-activated proton pump purified from the prokaryote Halobacterium halobium. The proteins are oriented as shown in the diagram. When ADP and Pi are added to the external medium and the vesicle is exposed to light, would this system produce ATP? Choose one: No, because protons are small enough to pass freely in and out of an artificial lipid vesicle. Yes, because the proton pump will generate a proton gradient that ATP synthase can use to synthesize ATP. No, because cows and prokaryotes are so distantly related that their proteins cannot be expected to work together. No, because ATP synthase is not oriented correctly. No, because no electron-transport chain is present.
No, because ATP synthase is not oriented correctly.
Below is a table listing the reactions that constitute the 10 steps of glycolysis, along with the change in free energy (ΔG°) for each step. Based on the data, which steps in glycolysis are effectively irreversible? Step Reaction ΔG (kJ/mol) 1 glucose + ATP → glucose 6-phosphate + ADP -34 2 glucose 6-phosphate → fructose 6-phosphate -2.9 3 fructose 6-phosphate + ATP → fructose 1,6-bisphosphate + ADP -19 4 fructose 1,6-bisphosphate → dihydroxyacetone phosphate + glyceraldehyde 3-phosphate -0.23 5 dihydroxyacetone phosphate → glyceraldehyde 3-phosphate 2.4 6 glyceraldehyde 3-phosphate + NAD+ + Pi → 1,3-bisphosphoglycerate + NADH -1.29 7 1,3-bisphosphoglycerate + ADP → 3-phosphoglycerate + ATP 0.09 8 3-phosphoglycerate → 2-phosphoglycerate 0.8 9 2-phosphoglycerate → phosphoenolpyruvate 1.1 10 phosphoenolpyruvate + ADP → pyruvate + ATP -23 Choose one: Steps 1, 3, 7, and 10 Step 1 Steps 1, 2, 3, 4, 6, and 10 Steps 1, 3, and 10 Steps 5, 7, 8, and 9 Steps 6 and 7
Steps 1, 3, and 10
Which of the following is true for eukaryotic cells? Choose one: Sugars and fats are both converted to acetyl CoA in the mitochondria. Sugars are converted to acetyl CoA, but fats are not. Sugars are converted to acetyl CoA in the mitochondria; fats are converted to acetyl CoA in the cytosol. Fats are converted to acetyl CoA in the mitochondria; sugars are converted to acetyl CoA in the cytosol. Fats are converted to acetyl CoA, but sugars are not.
Sugars and fats are both converted to acetyl CoA in the mitochondria.
What does it mean for a bond to be "high energy," such as the bonds between phosphate groups in ATP? Choose one: The hydrolysis of the bond is energetically favorable. The bond is strong and difficult to break. The bond is strong but breaks easily. The bond involves extra electrons. The hydrolysis of the bond is energetically unfavorable.
The hydrolysis of the bond is energetically favorable.
In what ways can mitochondria adapt to the changing needs of a cell? Choose one or more: They can change their location. They can change their number. They can change their shape. They can change their internal structure. They can carry out glycolysis.
They can change their location. They can change their number. They can change their shape.
In eukaryotic cells, why must metabolism be tightly regulated?Choose one: The substrates involved in metabolic reactions are each recognized by only a single, unique enzyme. Anabolic and catabolic pathways must compete for scarce resources. All metabolic reactions require energy. Anabolic and catabolic pathways must compete for oxygen. The substrates involved in metabolic reactions can be used by a number of different enzymes
The substrates involved in metabolic reactions can be used by a number of different enzymes
Diseases that disrupt the function of mitochondria are particularly harmful to muscle and nerve cells for what reason? Choose one: These cells undergo rapid cycles of cell division to function. These cells lack mitochondria. These cells need large amounts of ATP to function normally. These cells cannot produce energy by fermentation. These cells can produce energy by fermentation.
These cells need large amounts of ATP to function normally.
How do enzymes maximize the energy harvested from the oxidation of food molecules? Choose one: They allow the stepwise oxidation of food molecules, which releases energy in small amounts. They allow oxidation reactions to take place without an input of activation energy. They allow what would otherwise be an energetically unfavorable oxidation reaction to occur. They guarantee that each reaction involved in the oxidation of food molecules proceeds in just one direction. They allow a larger amount of energy to be released from food molecules such as glucose.
They allow the stepwise oxidation of food molecules, which releases energy in small amounts.
Why can electron carriers move a proton from one side of a membrane to the other? Choose one: They have a higher affinity for protons than does water. They have a redox potential higher than that of NADH. They can accept an electron (along with an H+ from water) on one side of the membrane and then release the H+ on the other side of the membrane as they pass the electron to the next carrier. They are able to invert their orientation within the membrane, allowing them to pick up a proton from one side of the membrane and release it on the other. They have a redox potential lower than that of NADH.
They can accept an electron (along with an H+ from water) on one side of the membrane and then release the H+ on the other side of the membrane as they pass the electron to the next carrier.
How does the photosynthetic machinery produce enough energy to transfer electrons from H2O to NADPH? Choose one: The proton gradient produced by electron transport powers the production of NADPH. The proton gradient produced by electron transport lowers the redox potential of H2O. ATP produced by photosystem II powers the synthesis of NADPH. Two photosystems operating in series couple their electron-energizing steps. Two photosystems operating in series generate enough light energy to produce NADPH.
Two photosystems operating in series couple their electron-energizing steps.
Which of the following describes a breakdown process in which enzymes degrade complex molecules into simpler ones? Choose one: anabolism metabolism catabolism Enzymes are not needed to break down complex molecules into simpler ones.
catabolism
The buildup of lactic and formic acids generated by anaerobic fermentation likely favored the evolution of which of the following?Choose one: cells that could pump protons hydrothermal vents multicellular life cells that could use the energy of sunlight to produce NADPH eukaryotic cells
cells that could pump protons
After an overnight fast, most of the acetyl CoA entering the citric acid cycle is derived from what type of molecule? Choose one: amino acids glucose fatty acids glycogen pyruvate
fatty acids
It is energetically favorable for protons to flow in which direction?Choose one: from the mitochondrial matrix to the intermembrane space from the intermembrane space to the mitochondrial matrix toward the compartment with the most positive charge across the outer mitochondrial membrane toward the compartment with the lowest pH
from the intermembrane space to the mitochondrial matrix
The chemistry of many metabolic reactions was deciphered using molecules labeled with radioactive isotopes. If acetyl CoA labeled with radioactive 14C in both carbon positions were fed into the citric acid cycle, where would the radioactivity be after one turn of the cycle? Choose one: in CO2 in acetyl CoA in oxaloacetate and in CO2 in oxaloacetate in citrate
in oxaloacetate
In an animal cell, where are the proteins of the electron-transport chain located? Choose one: plasma membrane outer mitochondrial membrane ER membrane mitochondrial matrix inner mitochondrial membrane
inner mitochondrial membrane
Which metal ion is found in all three respiratory enzyme complexes?Choose one: manganese iron heme sulfur copper
iron
The proton flow through the transmembrane H+ carrier of ATP synthase results in Choose one: mechanical rotation that is converted into the chemical-bond energy of ATP. bending of the carrier and stalk to produce mechanical force. moving ADP and Pi across the membrane into the enzyme active site. binding of the proton to ADP to enhance formation of the phosphate bond.
mechanical rotation that is converted into the chemical-bond energy of ATP.
Which molecules are required for the citric acid cycle to fully oxidize the carbons donated by acetyl CoA? Choose one or more: oxaloacetate ATP O2 GTP NAD+ GDP
oxaloacetate O2 NAD+ GDP
Which of the following is true when the concentrations of substrate and product are equal? Choose one: ΔG° = 0 ΔG = 0 The reaction is at equilibrium. ΔG = ΔG° ΔG° = K
ΔG = ΔG°
In cells that cannot carry out fermentation, which products derived from glycolysis will accumulate under anaerobic conditions? Choose one: glucose 6-phosphate and NADH pyruvate and NAD+ lactate and NAD+ pyruvate and NADH glucose and NADH
pyruvate and NADH
The synthesis of ATP in glycolysis occurs by which process? Choose one: a transfer of phosphate from AMP oxidative phosphorylation substrate-level dephosphorylation substrate-level phosphorylation a transfer of electrons from NADH
substrate-level phosphorylation
Glycolysis produces ___________ ATP molecules, whereas the complete oxidation of glucose to water and carbon dioxide produces ___________ ATP molecules. Choose one: four; twenty two; thirty two; ten four; thirty-four
two; thirty
