Chapter 8 & 9 Pretest questions
A mutation in yeast makes it unable to convert pyruvate to ethanol. How will this mutation affect these yeast cells? A. The mutant yeast will be unable to grow anaerobically. B. The mutant yeast will die because they cannot regenerate NAD+ from NAD. C. The mutant yeast will be unable to metabolize glucose. D. The mutant yeast will metabolize only fatty acids. E. The mutant yeast will grow anaerobically only when given glucose.
A
A solution of starch at room temperature does not readily decompose to form a solution of simple sugars because A. the activation energy barrier for this reaction cannot easily be surmounted at room temperature. B. starch cannot be hydrolyzed in the presence of so much water. C. starch hydrolysis is nonspontaneous. D. the starch solution has less free energy than the sugar solution. E. the hydrolysis of starch to sugar is endergonic.
A
ATP synthase is a key enzyme of mitochondrial energy conversion. Mitochondrial ATP synthase deficiency is due to a mutation in a gene important for the formation of a subunit in the ATP synthase complex. Scientists could use cells with this gene mutation to investigate which of the following questions? A. What effect does the mutation have on the amount of ATP synthesized during cellular respiration? B. What effect does the mutation have on the movement of electrons between the electron carriers of the electron transport chain? C. What effect does the mutation have on the number of protons pumped into the intermembrane space of the mitochondria? D. What effect does the mutation have on the number of water molecules formed at the end of the electron transport chain?
A
Allosteric enzyme regulation is usually associated with A. an enzyme with more than one subunit. B. lack of cooperativity. C. the need for cofactors. D. feedback inhibition. E. activating activity.
A
An important group of peripheral membrane proteins are enzymes such as the phospholipases that cleave the head groups of phospholipids. What properties must these enzymes exhibit? A. water solubility B. resistance to degradation C. lipid solubility D. membrane-spanning domains E. independence from cofactor interaction
A
An organism is discovered that thrives both in the presence and absence of oxygen in the air. Curiously, the consumption of sugar increases as oxygen is removed from the organism's environment, even though the organism does not gain much weight. This organism A. is a facultative anaerobe. B. is photosynthetic. C. is a normal eukaryotic organism. D. must use a molecule other than oxygen to accept electrons from the electron transport chain. E. is an anaerobic organism.
A
Chemiosmotic ATP synthesis (oxidative phosphorylation) occurs in A. all respiring cells, both prokaryotic and eukaryotic, using either oxygen or other electron acceptors. B. all cells, but only in the presence of oxygen. C. only in mitochondria, using either oxygen or other electron acceptors. D. all cells, in the absence of respiration. E. only eukaryotic cells, in the presence of oxygen.
A
Exposing inner mitochondrial membranes to ultrasonic vibrations will disrupt the membranes. However, the fragments will reseal "inside out." The little vesicles that result can still transfer electrons from NADH to oxygen and synthesize ATP. These inside-out membrane vesicles A. will become acidic inside the vesicles when NADH is added. B. will become alkaline inside the vesicles when NADH is added. C. will hydrolyze ATP to pump protons out of the interior of the vesicle to the exterior. D. will make ATP from ADP and i if transferred to a pH 4 buffered solution after incubation in a pH 7 buffered solution. E. will reverse electron flow to generate NADH from NAD+ in the absence of oxygen.
A
For the hydrolysis of ATP to ADP + i, the free energy change is -7.3 kcal/mol under standard conditions (1 M concentration of both reactants and products). In the cellular environment, however, the free energy change is about -13 kcal/mol. What can we conclude about the free energy change for the formation of ATP from ADP and i under cellular conditions? A. It is about +13 kcal/mol. B. It is greater than +13 kcal/mol. C. It is less than +7.3 kcal/mol. D. It is +7.3 kcal/mol. E. The information given is insufficient to deduce the free energy change.
A
How many carbon atoms are fed into the citric acid cycle as a result of the oxidation of one molecule of pyruvate? A. two B. six C. eight D. four E. ten
A
In a mitochondrion, if the matrix ATP concentration is high, and the intermembrane space proton concentration is too low to generate sufficient proton-motive force, then A. ATP synthase will hydrolyze ATP and pump protons into the intermembrane space. B. ATP synthase will increase the rate of ATP synthesis. C. ATP synthase will stop working. D. ATP synthase will hydrolyze ATP and pump protons into the matrix.
A
In chemiosmosis, what is the most direct source of energy that is used to convert ADP + A. energy released from movement of protons through ATP synthase, down their electrochemical gradient B. energy released from dehydration synthesis reactions C. energy released as electrons flow through the electron transport system D. energy released from substrate-level phosphorylation E. No external source of energy is required because the reaction is exergonic.
A
Increasing the substrate concentration in an enzymatic reaction could overcome which of the following? A. competitive inhibition B. insufficient cofactors C. saturation of the enzyme activity D. allosteric inhibition E. denaturation of the enzyme
A
Inside an active mitochondrion, most electrons follow which pathway? A. citric acid cycle → NADH → electron transport chain → oxygen B. citric acid cycle → FADH2 → electron transport chain → ATP C. pyruvate → citric acid cycle → ATP → NADH → oxygen D. glycolysis → NADH → oxidative phosphorylation → ATP → oxygen E. electron transport chain → citric acid cycle → ATP → oxygen
A
Mutations that result in single amino acid substitutions in an enzyme A. may change the enzyme's optimal temperature or optimal pH. B. will almost always destroy the activity of the enzyme. C. may, in rare cases, cause the enzyme to run reactions in reverse. D. cannot affect the activity or properties of the enzyme. E. will often change the substrate specificity of the enzyme.
A
New biosensors, applied like a temporary tattoo to the skin, can alert serious athletes that they are about to "hit the wall" and find it difficult to continue exercising. These biosensors monitor lactate, a form of lactic acid, released in sweat during strenuous exercise. Which of the statements below is the best explanation of why athletes would need to monitor lactate levels? A. During anaerobic respiration, lactate levels increase when muscles cells need more energy, however muscles cells eventually fatigue, thus athletes should modify their activities to increase aerobic respiration. B. During aerobic respiration, muscles cells produce too much lactate which causes a rise in the pH of the muscle cells, thus athletes must consume increased amounts of sports drinks, high in electrolytes, to buffer the pH. C. During aerobic respiration, muscle cells cannot produce enough lactate to fuel muscle cell contractions and muscles begin to cramp, thus athletic performance suffers. D. During anaerobic respiration, muscle cells receive too little oxygen and begin to convert lactate to pyruvate (pyruvic acid), thus athletes experience cramping and fatigue.
A
One function of both alcohol fermentation and lactic acid fermentation is to A. oxidize NADH to NAD+. B. reduce FADH2 to FAD+. C. reduce NAD+ to NADH. D. reduce FAD+ to FADH2. E. do none of the above.
A
Phosphofructokinase is an important control enzyme in the regulation of cellular respiration. Which of the following statements correctly describes phosphofructokinase activity? A. It is an allosteric enzyme. B. It is inhibited by AMP. C. It is activated by ATP. D. It is activated by citrate, an intermediate of the citric acid cycle. E. It catalyzes the conversion of fructose 1,6-bisphosphate to fructose 6-phosphate, an early step of glycolysis.
A
The ATP made during fermentation is generated by which of the following? A. substrate-level phosphorylation B. aerobic respiration C. oxidative phosphorylation D. the electron transport chain E. chemiosmosis
A
The figure shows the electron transport chain. Which of the following is the combination of substances that is initially added to the chain? A. NADH, FADH2, and O2 B. oxygen, carbon dioxide, and water C. NADH, FADH2, and protons D. NAD+, FAD, and electrons E. oxygen and protons
A
The primary role of oxygen in cellular respiration is to A. act as an acceptor for electrons and hydrogen, forming water. B. catalyze the reactions of glycolysis. C. combine with carbon, forming CO2. D. combine with lactate, forming pyruvate. E. yield energy in the form of ATP as it is passed down the respiratory chain.
A
What fraction of the carbon dioxide exhaled by animals is generated by the reactions of the citric acid cycle, if glucose is the sole energy source? A. 2/3 B. 1/3 C. 1/6 D. all of it E. 1/2
A
What happens at the end of the chain in the figure? A. 4 electrons combine with a molecule of oxygen and 4 protons. B. 4 electrons combine with four hydrogen and two oxygen atoms. C. 2 electrons combine with a molecule of oxygen and two hydrogen atoms. D. 2 electrons combine with a proton and a molecule of NAD+. E. 1 electron combines with a molecule of oxygen and a hydrogen atom.
A
What is proton-motive force? A. the force provided by a transmembrane hydrogen ion gradient B. the force that moves hydrogen into the mitochondrion C. the force required to remove an electron from hydrogen D. the force that moves hydrogen to NAD+ E. the force that moves hydrogen into the intermembrane space
A
What is the purpose of beta oxidation in respiration? A. breakdown of fatty acids B. feedback regulation C. oxidation of glucose D. oxidation of pyruvate E. control of ATP accumulation
A
When a molecule of NAD+ (nicotinamide adenine dinucleotide) gains a hydrogen atom (not a proton), the molecule becomes A. reduced. B. hydrolyzed. C. oxidized. D. dehydrogenated. E. redoxed.
A
When hydrogen ions are pumped from the mitochondrial matrix across the inner membrane and into the intermembrane space, the result is the A. creation of a proton-motive force. B. restoration of the Na+/K+ balance across the membrane. C. lowering of pH in the mitochondrial matrix. D. formation of ATP. E. reduction of NAD+.
A
Which catabolic processes may have been used by cells on ancient Earth before free oxygen became available? A. glycolysis, pyruvate oxidation, the citric acid cycle, and oxidative phosphorylation, using an electron acceptor other than oxygen B. oxidative phosphorylation only C. glycolysis, pyruvate oxidation, and the citric acid cycle D. glycolysis and fermentation only E. glycolysis and the citric acid cycle only
A
Which of the following best describes enthalpy (H)? A. the heat content of a chemical system B. the condition of a cell that is not able to react C. the cell's energy equilibrium D. the total kinetic energy of a system E. the system's entropy
A
Which of the following normally occurs regardless of whether or not oxygen (O2) is present? A. glycolysis B. fermentation C. oxidative phosphorylation (chemiosmosis) D. oxidation of pyruvate to acetyl CoA E. citric acid cycle
A
Which of the following represents the activation energy needed for the enzyme-catalyzed reverse reaction, C + D → A + B, in the figure? A. a B. b C. c D. d E. e
A
Which of the following statements is representative of the second law of thermodynamics? A. Cells require a continuous input of energy to maintain their high level of organization. B. Without an input of energy, organisms would tend toward decreasing entropy. C. Heat represents a form of energy that can be used by most organisms to do work. D. Conversion of energy from one form to another is always accompanied by some gain of free energy. E. Every energy transformation by a cell decreases the entropy of the universe.
A
Which statement best supports the hypothesis that glycolysis is an ancient metabolic pathway that originated before the last universal common ancestor of life on Earth? A. Glycolysis is widespread and is found in the domains Bacteria, Archaea, and Eukarya. B. Glycolysis is found in all eukaryotic cells. C. The enzymes of glycolysis are found in the cytosol rather than in a membrane-enclosed organelle. D. Glycolysis neither uses nor needs O2. E. Ancient prokaryotic cells, the most primitive of cells, made extensive use of glycolysis long before oxygen was present in Earth's atmosphere.
A
Zinc, an essential trace element for most organisms, is present in the active site of the enzyme carboxypeptidase. The zinc most likely functions as a(n) A. cofactor necessary for enzyme activity. B. allosteric activator of the enzyme. C. coenzyme derived from a vitamin. D. noncompetitive inhibitor of the enzyme. E. competitive inhibitor of the enzyme.
A
A chemical reaction that has a positive ΔG is best described as A. enthalpic. B. endergonic. C. exergonic. D. entropic E. spontaneous.
B
A number of systems for pumping ions across membranes are powered by ATP. Such ATP-powered pumps are often called ATPases although they don't often hydrolyze ATP unless they are simultaneously transporting ions. Because small increases in calcium ions in the cytosol can trigger a number of different intracellular reactions, cells keep the cytosolic calcium concentration quite low under normal conditions, using ATP-powered calcium pumps. For example, muscle cells transport calcium from the cytosol into the membranous system called the sarcoplasmic reticulum (SR). If a resting muscle cell's cytosol has a free calcium ion concentration of 10-7 while the concentration in the SR is 10-2, then how is the ATPase acting? A. ATPase activity must be opening a channel for the calcium ions to diffuse back into the SR along the concentration gradient. B. ATPase activity must be pumping calcium from the cytosol to the SR against the concentration gradient. C. ATPase activity must be powering an inflow of calcium from the outside of the cell into the SR. D. ATPase activity must be routing calcium ions from the SR to the cytosol, and then to the cell's environment. E. ATPase activity must be transferring i to the SR to enable this to occur.
B
A series of enzymes catalyze the reaction X → Y → Z → A. Product A binds to the enzyme that converts X to Y at a position remote from its active site. This binding decreases the activity of the enzyme. With respect to the enzyme that converts X to Y, substance A functions as A. a competitive inhibitor. B. an allosteric inhibitor. C. a coenzyme. D. the substrate. E. an intermediate.
B
An important group of peripheral membrane proteins are enzymes such as the phospholipases that cleave the head groups of phospholipids. What properties must these enzymes exhibit? A. membrane-spanning domains B. water solubility C. resistance to degradation D. independence from cofactor interaction E. lipid solubility
B
Besides turning enzymes on or off, what other means does a cell use to control enzymatic activity? A. connecting enzymes into large aggregates B. localization of enzymes into specific organelles or membranes C. cessation of cellular protein synthesis D. hydrophobic interactions E. exporting enzymes out of the cell
B
Biological systems use free energy based on empirical data that all organisms require a constant energy input. The first law of thermodynamics states that energy can be neither created nor destroyed. For living organisms, which of the following statements is an important consequence of this first law? A. Organisms are unable to transform energy from the different states in which it can exist. B. The organism must ultimately obtain all the necessary energy for life from its environment. C. The entropy of an organism decreases with time as the organism grows in complexity. D. The energy content of an organism is constant except for when its cells are dividing.
B
During glycolysis, when each molecule of glucose is catabolized to two molecules of pyruvate, most of the potential energy contained in glucose is A. used to phosphorylate fructose to form fructose 6-phosphate. B. retained in the two pyruvates. C. stored in the NADH produced. D. transferred directly to ATP. E. transferred to ADP, forming ATP.
B
During intense exercise, as skeletal muscle cells switch to fermentation, the human body will increase its catabolism of A. proteins only. B. carbohydrates only. C. fats only. D. fats and proteins only. E. fats, carbohydrates, and proteins.
B
Energy released by the electron transport chain is used to pump H+ into which location in eukaryotic cells? a. mitochondrial outer membrane b. mitochondrial intermembrane space c. mitochondrial matrix d. cytosol e. mitochondrial inner membrane
B
For each mole of glucose (C6H12O6) oxidized by cellular respiration, how many moles of CO2 are released in the citric acid cycle (see the figure)? A. 3 B. 4 C. 2 D. 12 E. 6
B
For each molecule of glucose that is metabolized by glycolysis and the citric acid cycle (see the figure), what is the total number of NADH + FADH2 molecules produced? A. 6 B. 12 C. 5 D. 10 E. 4
B
If a cell is able to synthesize 30 ATP molecules for each molecule of glucose completely oxidized to carbon dioxide and water, approximately how many ATP molecules can the cell synthesize for each molecule of pyruvate oxidized to carbon dioxide and water? A. 12 B. 14 C. 1 D. 26 E. 0
B
If pyruvate oxidation is blocked, what will happen to the levels of oxaloacetate and citric acid in the citric acid cycle shown in the figure? A. Oxaloacetate will decrease and citric acid will accumulate. B. Oxaloacetate will accumulate and citric acid will decrease. C. Both oxaloacetate and citric acid will decrease. D. Both oxaloacetate and citric acid will accumulate. E. There will be no change in the levels of oxaloacetate and citric acid.
B
In glycolysis, for each molecule of glucose oxidized to pyruvate A. four molecules of ATP are used and two molecules of ATP are produced. B. two molecules of ATP are used and four molecules of ATP are produced. C. six molecules of ATP are used and six molecules of ATP are produced. D. two molecules of ATP are used and six molecules of ATP are produced. E. two molecules of ATP are used and two molecules of ATP are produced.
B
In order to attach a particular amino acid to the tRNA molecule that will transport it, an enzyme, an aminoacyl-tRNA synthetase, is required, along with ATP. Initially, the enzyme has an active site for ATP and another for the amino acid, but it is not able to attach the tRNA. What must occur in order for the final attachment to occur? A. The 3' end of the tRNA must have to be cleaved before it can have an attached amino acid. B. The binding of the first two molecules must cause a 3-D change that opens another active site on the enzyme. C. The ATP must be hydrolyzed to allow the amino acid to bind to the synthetase. D. The tRNA molecule must have to alter its shape in order to be able to fit into the active site with the other two molecules. E. The ATP must first have to attach to the tRNA.
B
In vertebrate animals, brown fat tissue's color is due to abundant blood vessels and capillaries. White fat tissue, on the other hand, is specialized for fat storage and contains relatively few blood vessels or capillaries. Brown fat cells have a specialized protein that dissipates the proton-motive force across the mitochondrial membranes. Which of the following might be the function of the brown fat tissue? A. to allow other membranes of the cell to perform mitochondrial functions B. to regulate temperature by converting most of the energy from NADH oxidation to heat C. to allow the animals to regulate their metabolic rate when it is especially hot D. to increase the rate of oxidative phosphorylation from its few mitochondria E. to increase the production of ATP
B
Living organisms increase in complexity as they grow, resulting in a decrease in the entropy of an organism. How does this relate to the second law of thermodynamics? A. Life obeys the second law of thermodynamics because the decrease in entropy as the organism grows is exactly balanced by an increase in the entropy of the universe. B. As a consequence of growing, organisms cause a greater increase in entropy in their environment than the decrease in entropy associated with their growth. C. Living organisms do not follow the laws of thermodynamics. D. Living organisms are able to transform energy into entropy. E. Living organisms do not obey the second law of thermodynamics, which states that entropy must increase with time.
B
Succinate dehydrogenase catalyzes the conversion of succinate to fumarate. The reaction is inhibited by malonic acid, which resembles succinate but cannot be acted upon by succinate dehydrogenase. Increasing the ratio of succinate to malonic acid reduces the inhibitory effect of malonic acid. Based on this information, which of the following is correct? A. Succinate dehydrogenase is the enzyme, and malonic acid is the substrate. B. Succinate is the substrate, and fumarate is the product. C. Fumarate is the product, and malonic acid is a noncompetitive inhibitor. D. Succinate dehydrogenase is the enzyme, and fumarate is the substrate. E. Malonic acid is the product, and fumarate is a competitive inhibitor.
B
The ATP made during glycolysis is generated by A. chemiosmosis. B. substrate-level phosphorylation. C. photophosphorylation. D. electron transport. E. oxidation of NADH to NAD+.
B
The free energy for the oxidation of glucose to CO2 and water is -686 kcal/mol and the free energy for the reduction of NAD+ to NADH is +53 kcal/mol. Why are only two molecules of NADH formed during glycolysis when it appears that as many as a dozen could be formed? A. There is no CO2 or water produced as products of glycolysis. B. Most of the free energy available from the oxidation of glucose remains in pyruvate, one of the products of glycolysis. C. Most of the free energy available from the oxidation of glucose is used in the production of ATP in glycolysis. D. Glycolysis consists of many enzymatic reactions, each of which extracts some energy from the glucose molecule. E. Glycolysis is a very inefficient reaction, with much of the energy of glucose released as heat.
B
What is the difference (if any) between the structure of ATP and the structure of the precursor of the A nucleotide in RNA? A. The nitrogen-containing base is different. B. There is no difference. C. The number of phosphates is three instead of two. D. The number of phosphates is three instead of one. E. The sugar molecule is different.
B
When 10,000 molecules of ATP are hydrolyzed to ADP and i in a test tube, about half as much heat is liberated as when a cell hydrolyzes the same amount of ATP. Which of the following is the best explanation for this observation? A. Cells are open systems, but a test tube is an isolated system. B. Reactant and product concentrations in the test tube are different from those in the cell. C. The reaction in cells must be catalyzed by enzymes, but the reaction in a test tube does not need enzymes. D. Cells are less efficient at heat production than nonliving systems. E. The hydrolysis of ATP in a cell produces different chemical products than does the reaction in a test tube.
B
When chemical, transport, or mechanical work is done by an organism, what happens to the heat generated? A. It is used to generate ADP from nucleotide precursors. B. It is lost to the environment. C. It is transported to specific organs such as the brain. D. It is used to power yet more cellular work. E. It is used to store energy as more ATP.
B
Where are the proteins of the electron transport chain located? A. mitochondrial outer membrane B. mitochondrial inner membrane C. mitochondrial matrix D. mitochondrial intermembrane space E. cytosol
B
Which metabolic pathway is common to both cellular respiration and fermentation? A. the citric acid cycle B. glycolysis C. the oxidation of pyruvate to acetyl CoA D. chemiosmosis E. oxidative phosphorylation
B
Which of the following is a statement of the first law of thermodynamics? The entropy of the universe is decreasing. A. Energy cannot be transferred or transformed. B. Energy cannot be created or destroyed. C. Kinetic energy is stored energy that results from the specific arrangement of matter. D. The entropy of the universe is constant.
B
Which of the following is an example of potential rather than kinetic energy? A.water rushing over Niagara Falls B. a molecule of glucose C. the muscle contractions of a person mowing grass D. light flashes emitted by a firefly E. the flight of an insect foraging for food
B
Which of the following represents the activation energy required for the enzyme-catalyzed reaction in the figure? A. a B. b C. c D. d E. e
B
Which of the following statements is true concerning catabolic pathways? A. They are spontaneous and do not need enzyme catalysis. B. They supply energy, primarily in the form of ATP, for the cell's work. C. They are endergonic. D. They build up complex molecules such as protein from simpler compounds. E. They combine molecules into more energy-rich molecules.
B
According to the induced fit hypothesis of enzyme catalysis, which of the following is correct? A. Some enzymes change their structure when activators bind to the enzyme. B. The binding of the substrate depends on the shape of the active site. C. The binding of the substrate changes the shape of the enzyme's active site. D. A competitive inhibitor can outcompete the substrate for the active site. E. The active site creates a microenvironment ideal for the reaction.
C
Activity of various enzymes at various temperatures (a) and at various pH (b). Which temperature and pH profile curves on the graphs were most likely generated from analysis of an enzyme from a human stomach where conditions are strongly acid? A. curves 3 and 4 B. curves 2 and 5 C. curves 1 and 4 D. curves 1 and 5 E. curves 2 and 4
C
An electron loses potential energy when it A. shifts to a less electronegative atom. B. moves further away from the nucleus of the atom. C. shifts to a more electronegative atom. D. increases its kinetic energy. E. increases its activity as an oxidizing agent.
C
Chemical equilibrium is relatively rare in living cells. Which of the following could be an example of a reaction at chemical equilibrium in a cell? A. an endergonic reaction in an active metabolic pathway where the energy for that reaction is supplied only by heat from the environment B. a chemical reaction in which the entropy change in the reaction is just balanced by an opposite entropy change in the cell's surroundings C. a chemical reaction in which both the reactants and products are not being produced or used in any active metabolic pathway at that time in the cell D. no possibility of having chemical equilibrium in any living cell E. a reaction in which the free energy at equilibrium is higher than the energy content at any point away from equilibrium
C
During a laboratory experiment, you discover that an enzyme-catalyzed reaction has a G of -20 kcal/mol. If you double the amount of enzyme in the reaction, what will be the G for the new reaction? A. -40 kcal/mol B. 0 kcal/mol C. -20 kcal/mol D. +40 kcal/mol E. +20 kcal/mol
C
Even though plants cells photosynthesize, they still use their mitochondria for oxidation of pyruvate. When and where will this occur? A. in cells that are storing glucose only B. in nonphotosynthesizing cells only C. in all cells all the time D. in photosynthesizing cells in the light and in other tissues in the dark E. in photosynthetic cells in the light, while photosynthesis occurs concurrently
C
How many oxygen molecules (O2) are required each time a molecule of glucose (C6H12O6) is completely oxidized to carbon dioxide and water via aerobic respiration,? A. 12 B. 1 C. 6 D. 3 E. 30
C
In liver cells, the inner mitochondrial membranes are about five times the area of the outer mitochondrial membranes. What purpose must this serve? A. It allows the liver cell to have fewer mitochondria. B. It allows for an increased rate of glycolysis. C. It increases the surface for oxidative phosphorylation. D. It increases the surface for substrate-level phosphorylation. E. It allows for an increased rate of the citric acid cycle.
C
Protein kinases are enzymes that catalyze phosphorylation of target proteins at specific sites, whereas protein phosphatases catalyze removal of phosphate(s) from phosphorylated proteins. Phosphorylation and dephosphorylation can function as an on-off switch for a protein's activity, most likely through A. the excision of one or more peptides. B. a change in the optimal pH at which a reaction will occur. C. the change in a protein's charge leading to a conformational change. D. the change in a protein's charge leading to cleavage. E. a change in the optimal temperature at which a reaction will occur.
C
Protein kinases are enzymes that transfer the terminal phosphate from ATP to an amino acid residue on the target protein. Many are located on the plasma membrane as integral membrane proteins or peripheral membrane proteins. What purpose may be served by their plasma membrane localization? A. ATP is more abundant near the plasma membrane. B. Membrane localization lowers the activation energy of the phosphorylation reaction. C. They can more readily encounter and phosphorylate other membrane proteins. D. They require phospholipids as a cofactor. E. They flip back and forth across the membrane to access target proteins on either side.
C
Some of the drugs used to treat HIV patients are competitive inhibitors of the HIV reverse transcriptase enzyme. Unfortunately, the high mutation rate of HIV means that the virus rapidly acquires mutations with amino acid changes that make them resistant to these competitive inhibitors. Where in the reverse transcriptase enzyme would such amino acid changes most likely occur in drug-resistant viruses? A. such mutations could occur anywhere with equal probability B. in regions of the protein that determine packaging into the virus capsid C. in or near the active site D. at a cofactor binding site E. at an allosteric site
C
Substrate-level phosphorylation accounts for approximately what percentage of the ATP formed by the reactions of glycolysis? A. 0% B. 2% C. 100% D. 38% E. 10%
C
Succinate dehydrogenase catalyzes the conversion of succinate to fumarate. The reaction is inhibited by malonic acid, which resembles succinate but cannot be acted upon by succinate dehydrogenase. Increasing the ratio of succinate to malonic acid reduces the inhibitory effect of malonic acid. What is malonic acid's role with respect to succinate dehydrogenase? A. It is a noncompetitive inhibitor. B. It is able to bind to succinate. C. It is a competitive inhibitor. D. It is an allosteric regulator. E. It blocks the binding of fumarate.
C
The active site of an enzyme is the region that A. binds noncompetitive inhibitors of the enzyme. B. is inhibited by the presence of a coenzyme or a cofactor. C. is involved in the catalytic reaction of the enzyme. D. binds allosteric regulators of the enzyme.
C
The mathematical expression for the change in free energy of a system is ΔG =ΔH - TΔS. Which of the following is (are) correct? A. ΔS is the change in enthalpy, a measure of randomness. B. T is the temperature in degrees Celsius. C. ΔG is the change in free energy. D. ΔH is the change in entropy, the energy available to do work.
C
The mechanism in which the end product of a metabolic pathway inhibits an earlier step in the pathway is most precisely described as A. metabolic inhibition. B. reversible inhibition. C. feedback inhibition. D. noncooperative inhibition. E. allosteric inhibition.
C
The oxidation of glucose in the presence of oxygen involves glycolysis, pyruvate oxidation, and the citric acid cycle (Krebs cycle). Some energy is captured in glycolysis when glucose is converted to pyruvate (pyruvic acid). In the citric acid cycle (Krebs cycle), more energy is captured in the form of reduced electron carriers, NADH and FADH2. Select the best explanation for why the eventual reoxidation of NADH and FADH2 is crucial for the continuation of the citric acid (Krebs) cycle. A. The presence of reduced forms of the electron carriers prevents the formation of ATP. B. Phosphate cannot attach to ADP to form ATP without oxidized electron carriers. C. In order for the cycle to continue, oxidized electron carriers must be available. D. Without oxidized electron carriers, oxygen will not accept the electrons at the end of the electron transport chain.
C
The synthesis of ATP by oxidative phosphorylation, using the energy released by movement of protons across the membrane down their electrochemical gradient, is an example of A. allosteric regulation. B. active transport. C. an endergonic reaction coupled to an exergonic process. D. osmosis. E. a reaction with a positive ΔG .
C
When ATP releases some energy, it also releases inorganic phosphate. What happens to the inorganic phosphate in the cell? A. It is added to water and excreted as a liquid. B. It is used only to regenerate more ATP. C. It may be used to form a phosphorylated intermediate. D. It enters the nucleus and affects gene expression. E. It is secreted as waste.
C
When an individual is exercising heavily and when the muscle becomes oxygen-deprived, muscle cells convert pyruvate to lactate. What happens to the lactate in skeletal muscle cells? A. It is converted to NAD+. B. It produces CO2 and water. C. It is taken to the liver and converted back to pyruvate. D. It is converted to alcohol. E. It reduces FADH2 to FAD+.
C
Where is ATP synthase located in the mitochondrion? A. cytosol B. electron transport chain C. inner membrane D. mitochondrial matrix E. outer membrane
C
Which of the following is an example of cooperativity? A. one enzyme in a metabolic pathway passing its product to act as a substrate for the next enzyme in the pathway B. binding of an ATP molecule along with one of the substrate molecules in an active site C. a molecule binding at one unit of a tetramer, allowing faster binding at each of the other three D. the effect of increasing temperature on the rate of an enzymatic reaction E. the binding of an end product of a metabolic pathway to the first enzyme that acts in the pathway
C
Which of the following is true for all exergonic reactions? A. The products have more total energy than the reactants. B. The reaction goes only in a forward direction: all reactants will be converted to products, but no products will be converted to reactants. C. The reaction proceeds with a net release of free energy. D. The reactions are rapid. E. A net input of energy from the surroundings is required for the reactions to proceed.
C
Which of the following represents the activation energy required for a noncatalyzed reaction in the figure? A. a B. b C. c D. d E. e
C
Which of the following statements is a logical consequence of the second law of thermodynamics? A. Every energy transfer requires activation energy from the environment. B. If there is an increase in the energy of a system, there must be a corresponding decrease in the energy of the rest of the universe. C. Every chemical reaction must increase the total entropy of the universe. D. Energy can be transferred or transformed, but it cannot be created or destroyed. E. If the entropy of a system increases, there must be a corresponding decrease in the entropy of the universe.
C
Which of the following statements is true about enzyme-catalyzed reactions? A. Enzyme-catalyzed reactions require energy to activate the enzyme. B. The free energy change of the reaction is opposite from the reaction that occurs in the absence of the enzyme. C. The reaction is faster than the same reaction in the absence of the enzyme. D. The reaction always goes in the direction toward chemical equilibrium. E. Enzyme-catalyzed reactions release more free energy than noncatalyzed reactions.
C
Which of the following statements regarding enzymes is true? A. Enzymes increase the rate of a reaction by reducing the rate of reverse reactions. B. Enzymes change the equilibrium point of the reactions they catalyze. C. Enzymes increase the rate of a reaction by lowering the activation energy barrier. D. Enzymes increase the rate of a reaction by making the reaction more exergonic. E. Enzymes make the rate of a reaction independent of substrate concentrations.
C
Which of the following types of reactions would decrease the entropy within a cell? A. digestion B. hydrolysis C. anabolic reactions D. respiration E. catabolic reactions
C
Which process in eukaryotic cells will proceed normally whether oxygen (O2) is present or absent? A. the citric acid cycle B. electron transport C. glycolysis D. oxidative phosphorylation E. chemiosmosis
C
Which term most precisely describes the cellular process of breaking down large molecules into smaller ones? A. catalysis B. metabolism C. catabolism D. anabolism E. dehydration
C
Why is ATP an important molecule in metabolism? A. It is one of the four building blocks for DNA synthesis. B. Its terminal phosphate bond has higher energy than the other two. C. It provides energy coupling between exergonic and endergonic reactions. D. Its terminal phosphate group contains a strong covalent bond that, when hydrolyzed, releases free energy. E. Its hydrolysis provides an input of free energy for exergonic reactions.
C
A molecule that is phosphorylated A. has been reduced as a result of a redox reaction involving the loss of an inorganic phosphate. B. has a decreased chemical reactivity; it is less likely to provide energy for cellular work. C. has been oxidized as a result of a redox reaction involving the gain of an inorganic phosphate. D. has an increased chemical potential energy; it is primed to do cellular work. E. has less energy than before its phosphorylation and therefore less energy for cellular work.
D
A series of enzymes catalyze the reaction X → Y → Z → A. Product A binds to the enzyme that converts X to Y at a position remote from its active site. This binding decreases the activity of the enzyme. What is substance X? A. the product B. an allosteric inhibitor C. a coenzyme D. a substrate E. an intermediate
D
A system at chemical equilibrium A. releases energy at a steady rate. B. consumes energy at a steady rate. C. has zero kinetic energy. D. can do no work. E. consumes or releases energy, depending on whether it is exergonic or endergonic.
D
Activity of various enzymes at various temperatures (a) and at various pH (b). Which curve(s) on the graphs may represent the temperature and pH profiles of an enzyme taken from a bacterium that lives in a mildly alkaline hot springs at temperatures of 70°C or higher? A. curves 1 and 5 B. curves 2 and 4 C. curves 3 and 4 D. curves 3 and 5 E. curves 2 and 5
D
Approximately how many molecules of ATP are produced from the complete oxidation of two molecules of glucose (C6H12O6) in aerobic cellular respiration? A. 15 B. 2 C. 30-32 D. 60-64 E. 4
D
Besides turning enzymes on or off, what other means does a cell use to control enzymatic activity? A. connecting enzymes into large aggregates B. hydrophobic interactions C. cessation of cellular protein synthesis D. localization of enzymes into specific organelles or membranes E. exporting enzymes out of the cell
D
During aerobic respiration, H2O is formed. Where does the oxygen atom for the formation of the water come from? A. glucose (C6H12O6) B. pyruvate (C3H3O3−) C. carbon dioxide (CO2) D. molecular oxygen (O2) E. lactate (C3H3O3−)
D
During aerobic respiration, electrons travel downhill in which sequence? A. glucose → ATP → electron transport chain → NADH B. food → glycolysis → citric acid cycle → NADH → ATP C. glucose → pyruvate → ATP → oxygen D. food → NADH → electron transport chain → oxygen E. food → citric acid cycle → ATP → NAD+
D
During aerobic respiration, which of the following directly donates electrons to the electron transport chain at the lowest energy level? A. NAD+ B. ATP C. NADH D. FADH2 E. ADP + Pi
D
During cellular respiration, acetyl CoA accumulates in which location? A. mitochondrial intermembrane space B. cytosol C. mitochondrial inner membrane D. mitochondrial matrix E. mitochondrial outer membrane
D
Exposing inner mitochondrial membranes to ultrasonic vibrations will disrupt the membranes. However, the fragments will reseal "inside out." The little vesicles that result can still transfer electrons from NADH to oxygen and synthesize ATP. After the disruption, when electron transfer and ATP synthesis still occur, what must be present? A. all of the electron transport system and the ability to add CoA to acetyl groups B. the electron transport system C. the ATP synthase system D. all of the electron transport proteins as well as ATP synthase E. plasma membranes like those bacteria use for respiration
D
For living organisms, which of the following is an important consequence of the first law of thermodynamics? A. Life does not obey the first law of thermodynamics. B. The energy content of an organism is constant. C. Organisms grow by converting energy into organic matter. D. The organism ultimately must obtain all of the necessary energy for life from its environment. E. The entropy of an organism decreases with time as the organism grows in complexity.
D
High levels of citric acid inhibit the enzyme phosphofructokinase, a key enzyme in glycolysis. Citric acid binds to the enzyme at a different location from the active site. This is an example of A. the specificity of enzymes for their substrates. B. positive feedback regulation. C. competitive inhibition. D. allosteric regulation. E. an enzyme requiring a cofactor.
D
How does a noncompetitive inhibitor decrease the rate of an enzyme reaction? A. by decreasing the activation energy of the reaction B. by binding at the active site of the enzyme C. by changing the free energy change of the reaction D. by changing the shape of the enzyme's active site E. by acting as a coenzyme for the reaction
D
In a biological reaction, succinate dehydrogenase catalyzes the conversion of succinate to fumarate. The reaction is inhibited by malonic acid, a substance that resembles succinate but cannot be acted upon by succinate dehydrogenase. Increasing the amount of succinate molecules to those of malonic acid reduces the inhibitory effect if malonic acid. Select the correct identification of the molecules described in the reaction. A.Succinate dehydrogenase is the enzyme, and fumarate is the substrate in the reaction. B. Fumarate is the product, and malonic acid is a noncompetitive inhibitor in the reaction. C. Succinate dehydrogenase is the enzyme, and malonic acid is the substrate in the reaction. D. Succinate is the substrate, and fumarate is the product in the reaction.
D
In addition to ATP, what are the end products of glycolysis? A. CO2 and H2O B. H2O, FADH2, and citrate C. CO2 and pyruvate D. NADH and pyruvate E. CO2 and NADH
D
In alcohol fermentation, NAD+ is regenerated from NADH by A. reduction of pyruvate to form lactate. B. oxidation of pyruvate to acetyl CoA. C. oxidation of ethanol to acetyl CoA. D. reduction of acetaldehyde to ethanol (ethyl alcohol). E. reduction of ethanol to pyruvate.
D
In prokaryotes, the respiratory electron transport chain is located A. in the mitochondrial inner membrane. B. in the cytoplasm. C. in the bacterial outer membrane. D. in the plasma membrane. E. in the mitochondrial outer membrane.
D
In the absence of oxygen, yeast cells can obtain energy by fermentation, resulting in the production of A. ATP, pyruvate, and acetyl CoA. B. ATP, CO2, and lactate. C. ATP, NADH, and pyruvate. D. ATP, CO2, and ethanol (ethyl alcohol). E. ATP, pyruvate, and oxygen.
D
It is possible to prepare vesicles from portions of the inner mitochondrial membrane. Which one of the following processes might still be carried on by this isolated inner membrane? A. glycolysis and fermentation B. the citric acid cycle C. reduction of NAD+ D. oxidative phosphorylation E. both the citric acid cycle and oxidative phosphorylation
D
Phosphofructokinase is an allosteric enzyme that catalyzes the conversion of fructose 6-phosphate to fructose 1,6-bisphosphate, an early step of glycolysis. In the presence of oxygen, an increase in the amount of ATP in a cell would be expected to A. inhibit the enzyme and thus increase the rates of glycolysis and the citric acid cycle. B. activate the enzyme and increase the rates of glycolysis and the citric acid cycle. C. inhibit the enzyme and thus increase the rate of glycolysis and the concentration of citrate. D. inhibit the enzyme and thus slow the rates of glycolysis and the citric acid cycle. E. activate the enzyme and thus slow the rates of glycolysis and the citric acid cycle.
D
Protein kinases are enzymes that catalyze phosphorylation of target proteins at specific sites, whereas protein phosphatases catalyze removal of phosphate(s) from phosphorylated proteins. Phosphorylation and dephosphorylation can function as an on-off switch for a protein's activity, most likely through A. the excision of one or more peptides. B. a change in the optimal temperature at which a reaction will occur. C. the change in a protein's charge leading to cleavage. D. the change in a protein's charge leading to a conformational change. E. a change in the optimal pH at which a reaction will occur.
D
Starting with citrate, which of the following combinations of products would result from three acetyl CoA molecules entering the citric acid cycle (see the figure)? A. 38 ATP, 6 CO2, 3 NADH, and 12 FADH2 B. 2 ATP, 2 CO2, 3 NADH, and 3 FADH2 C. 1 ATP, 2 CO2, 3 NADH, and 1 FADH2 D. 3 ATP, 6 CO2, 9 NADH, and 3 FADH2 E. 3 ATP, 3 CO2, 3 NADH, and 3 FADH2
D
Starting with one molecule of glucose, the energy-containing products of glycolysis are A. 2 FADH2, 2 pyruvate, and 4 ATP. B. 2 NAD+, 2 pyruvate, and 2 ATP. C. 6 CO2, 2 pyruvate, and 30 ATP. D. 2 NADH, 2 pyruvate, and 2 ATP. E. 6 CO2, 2 pyruvate, and 2 ATP.
D
Starting with one molecule of isocitrate and ending with fumarate, how many ATP molecules can be made through substrate-level phosphorylation (see the figure)? A. 2 B. 12 C. 11 D. 1 E. 24
D
The direct energy source that drives ATP synthesis during respiratory oxidative phosphorylation in eukaryotic cells is A. oxidation of glucose to CO2 and water. B. the thermodynamically favorable transfer of phosphate from glycolysis and the citric acid cycle intermediate molecules of ADP. C. the thermodynamically favorable flow of electrons from NADH to the mitochondrial electron transport carriers. D. the proton-motive force across the inner mitochondrial membrane. E. the final transfer of electrons to oxygen.
D
What carbon sources can yeast cells metabolize to make ATP from ADP under anaerobic conditions? A. either ethanol or lactic acid B. pyruvate C. ethanol D. glucose E. lactic acid
D
When you have a severe fever, what grave consequence may occur if the fever is not controlled? A. removal of amine groups from your proteins B. removal of the amino acids in active sites of your enzymes C. binding of your enzymes to inappropriate substrates D. change in the tertiary structure of your enzymes E. destruction of your enzymes' primary structure
D
Which of the following in the figure would be the same in either an enzyme-catalyzed or a noncatalyzed reaction? A. a B. b C. c D. d E. e
D
Which of the following is (are) true for anabolic pathways? A. They do not depend on enzymes. B. They are usually highly spontaneous chemical reactions. C. They release energy as they degrade polymers to monomers. D. They consume energy to build up polymers from monomers. E. They consume energy to decrease the entropy of the organism and its environment.
D
Which of the following is an example of cooperativity? A. one enzyme in a metabolic pathway passing its product to act as a substrate for the next enzyme in the pathway B. the binding of an end product of a metabolic pathway to the first enzyme that acts in the pathway C. binding of an ATP molecule along with one of the substrate molecules in an active site D. a molecule binding at one unit of a tetramer, allowing faster binding at each of the other three E. the effect of increasing temperature on the rate of an enzymatic reaction
D
Which of the following is true of enzymes? A. Nonprotein cofactors alter the substrate specificity of enzymes. B. Enzyme function is increased if the 3-D structure or conformation of an enzyme is altered. C. Enzymes increase the rate of chemical reaction by providing activation energy to the substrate. D. Enzymes increase the rate of chemical reaction by lowering activation energy barriers. E. Enzyme function is independent of physical and chemical environmental factors such as pH and temperature.
D
Which of the following most accurately describes what is happening along the electron transport chain in the figure? A. Molecules in the chain give up some of their potential energy. B. Energy of the electrons increases at each step. C. ATP is generated at each step. D. Each electron carrier alternates between being reduced and being oxidized. E. Chemiosmosis is coupled with electron transfer.
D
Which of the following occurs in the cytosol of a eukaryotic cell? A. oxidation of pyruvate to acetyl CoA B. citric acid cycle C. oxidative phosphorylation D. glycolysis and fermentation E. fermentation and chemiosmosis
D
Which of the following produces the most ATP when glucose (C6H12O6) is completely oxidized to carbon dioxide (CO2) and water? A. glycolysis B. citric acid cycle C. oxidation of pyruvate to acetyl CoA D. oxidative phosphorylation (chemiosmosis) E. fermentation
D
Which of the following represents the difference between the free-energy content of the reactants and the free-energy content of the products in the figure? A. a B. b C. c D. d E. e
D
Which of the following represents the difference between the free-energy content of the reaction and the free-energy content of the products in the figure? A. a B. b C. c D. d E. e
D
Which of the following represents the ΔG of the reaction in the figure? A. a B. b C. c D. d E. e
D
Which of the following statements describes NAD+? A. NAD+ has more chemical energy than NADH. B. NAD+ can donate electrons for use in oxidative phosphorylation. C. NAD+ is oxidized by the action of hydrogenases. D. NAD+ is reduced to NADH during glycolysis, pyruvate oxidation, and the citric acid cycle. E. In the absence of NAD+, glycolysis can still function.
D
Which of the following statements describes enzyme cooperativity? A. Several substrate molecules can be catalyzed by the same enzyme. B. A substrate binds to an active site and inhibits cooperation between enzymes in a pathway. C. A product of a pathway serves as a competitive inhibitor of an early enzyme in the pathway. D. A substrate molecule bound to an active site of one subunit promotes substrate binding to the active site of other subunits. E. A multienzyme complex contains all the enzymes of a metabolic pathway.
D
Which of the following statements describes the results of this reaction? C6H12O6 + 6 O2 → 6 CO2 + 6 H2O + Energy A. O2 is reduced and CO2 is oxidized. B. C6H12O6 is reduced and CO2 is oxidized. C. O2 is oxidized and H2O is reduced. D. C6H12O6 is oxidized and O2 is reduced. E. CO2 is reduced and O2 is oxidized.
D
Which of the following terms best describes the forward reaction in the figure? A. endergonic,ΔG > 0 B. exergonic,ΔG > 0 C. chemical equilibrium,ΔG = 0 D. exergonic, Δ G < 0 E. endergonic,ΔG < 0
D
Which of the protein complexes labeled with Roman numerals in the figure will transfer electrons to O2? A. complex I B. complex II C. complex III D. complex IV E. All of the complexes can transfer electrons to O2.
D
Which one of the following is formed by the removal of a carbon (as CO2) from a molecule of pyruvate? A. glyceraldehyde-3-phosphate B. lactate C. oxaloacetate D. acetyl CoA E. citrate
D
Why is glycolysis described as having an investment phase and a payoff phase? A. It shifts molecules from cytosol to mitochondrion. B. It uses glucose and generates pyruvate. C. It both splits molecules and assembles molecules. D. It uses stored ATP and then forms a net increase in ATP. E. It attaches and detaches phosphate groups.
D
A young animal has never had much energy. He is brought to a veterinarian for help and is sent to the animal hospital for some tests. There they discover his mitochondria can use only fatty acids and amino acids for respiration, and his cells produce more lactate than normal. Of the following, which is the best explanation of his condition? A. His cells have a defective electron transport chain, so glucose goes to lactate instead of to acetyl CoA. B. His cells cannot move NADH from glycolysis into the mitochondria. C. His cells contain something that inhibits oxygen use in his mitochondria. D. His cells lack the enzyme in glycolysis that forms pyruvate. E. His mitochondria lack the transport protein that moves pyruvate across the outer mitochondrial membrane.
E
A young dog has never had much energy. He is brought to a veterinarian for help and she decides to conduct several diagnostic tests. She discovers that the dog's mitochondria can use only fatty acids and amino acids for respiration, and his cells produce more lactate than normal. Of the following, which is the best explanation of the dog's condition? A. His cells have a defective electron transport chain, so glucose goes to lactate instead of to acetyl CoA. B. His cells cannot move NADH from glycolysis into the mitochondria. C. His cells lack the enzyme in glycolysis that forms pyruvate. D. His cells contain something that inhibits oxygen use in his mitochondria. E. His mitochondria lack the transport protein that moves pyruvate across the outer mitochondrial membrane.
E
Biological evolution of life on Earth, from simple prokaryote-like cells to large, multicellular eukaryotic organisms, A. has been made possible by expending Earth's energy resources. B. has caused an increase in the entropy of the planet. C. has occurred in accordance with the laws of thermodynamics. D. violates the laws of thermodynamics because Earth is a closed system. E. has occurred in accordance with the laws of thermodynamics, by expending Earth's energy resources and causing an increase in the entropy of the planet.
E
Brown fat cells produce a protein called thermogenin in their mitochondrial inner membrane. Thermogenin is a channel for facilitated transport of protons across the membrane. What will occur in the brown fat cells when they produce thermogenin? A. ATP synthesis and heat generation will both increase. B. ATP synthesis and heat generation will stay the same. C. ATP synthesis and heat generation will both decrease. D. ATP synthesis will increase, and heat generation will decrease. E. ATP synthesis will decrease, and heat generation will increase.
E
Carbon dioxide (CO2) is released during which of the following stages of cellular respiration? A. fermentation and glycolysis B. oxidative phosphorylation and fermentation C. the citric acid cycle and oxidative phosphorylation D. glycolysis and the oxidation of pyruvate to acetyl CoA E. oxidation of pyruvate to acetyl CoA and the citric acid cycle
E
Carbon skeletons for amino acid biosynthesis are supplied by intermediates of the citric acid cycle. Which intermediate would supply the carbon skeleton for synthesis of a five-carbon amino acid (see the figure)? A. malate B. isocitrate C. citrate D. succinate E. α-ketoglutarate
E
How do cells use the ATP cycle shown in the figure? A. Cells use the cycle to generate or consume water molecules as needed. B. Cells use the cycle primarily to generate heat. C. Cells use the cycle to recycle energy released by ATP hydrolysis. D. Cells use the cycle to recycle ADP, phosphate, and the energy released by ATP hydrolysis. E. Cells use the cycle to recycle ADP and phosphate.
E
How does the pyruvate produced by glycolysis enter the mitochondrion? A. through a pore B. through a channel C. facilitated diffusion D. diffusion E. active transport
E
In cellular respiration, the energy for most ATP synthesis is supplied by A. generating carbon dioxide and oxygen in the electron transport chain. B. transferring electrons from organic molecules to pyruvate. C. high energy phosphate bonds in organic molecules. D. converting oxygen to ATP. E. a proton gradient across a membrane.
E
In the presence of oxygen, the three-carbon compound pyruvate can be catabolized in the citric acid cycle. First, however, the pyruvate (1) loses a carbon, which is given off as a molecule of CO2, (2) is oxidized to form a two-carbon compound called acetate, and (3) is bonded to coenzyme A. How does the addition of coenzyme A, a sulfur-containing molecule derived from a B vitamin, function in the subsequent reaction? A. It utilizes this portion of a B vitamin, which would otherwise be a waste product from another pathway. B. It drives the reaction that regenerates NAD+. C. It removes one molecule of CO2. D. It provides the sulfur needed for the molecule to enter the mitochondrion. E. It provides a relatively unstable molecule whose acetyl portion can be readily transferred to a compound in the citric acid cycle.
E
In the presence of oxygen, the three-carbon compound pyruvate can be catabolized in the citric acid cycle. First, however, the pyruvate (1) loses a carbon, which is given off as a molecule of CO2, (2) is oxidized to form a two-carbon compound called acetate, and (3) is bonded to coenzyme A. These three steps result in the formation of A. acetyl CoA, FADH2, and CO2. B. acetyl CoA, NAD+, ATP, and CO2. C. acetyl CoA, O2, and ATP. D. acetyl CoA, FAD, O2, and CO2. E. acetyl CoA, NADH, H+, and CO2.
E
Reactants capable of interacting to form products in a chemical reaction must first overcome a thermodynamic barrier known as the reaction's A. equilibrium point. B. free-energy content. C. entropy. D. endothermic level. E. activation energy.
E
The molecule that functions as the reducing agent (electron donor) in a redox or oxidation-reduction reaction A. neither gains nor loses electrons, but gains or loses potential energy. B. loses electrons and gains potential energy. C. gains electrons and loses potential energy. D. gains electrons and gains potential energy. E. loses electrons and loses potential energy.
E
The oxygen consumed during cellular respiration is involved directly in which process or event? A. the citric acid cycle B. the phosphorylation of ADP to form ATP C. the oxidation of pyruvate to acetyl CoA D. glycolysis E. accepting electrons at the end of the electron transport chain
E
What is the term for metabolic pathways that release stored energy by breaking down complex molecules? A. anabolic pathways B. bioenergetic pathways C. thermodynamic pathways D. fermentation pathways E. catabolic pathways
E
When a glucose molecule loses a hydrogen atom as the result of an oxidation-reduction reaction, the molecule becomes A. hydrolyzed. B. an oxidizing agent. C. reduced. D. hydrogenated. E. oxidized.
E
When electrons move closer to a more electronegative atom, what happens? A. The more electronegative atom is oxidized, and energy is consumed. B. The more electronegative atom is oxidized, and energy is released. C. The more electronegative atom is reduced, and entropy decreases. D. The more electronegative atom is reduced, and energy is consumed. E. The more electronegative atom is reduced, and energy is released.
E
Whenever energy is transformed, there is always an increase in the A. free energy of the universe. B. entropy of the system. C. free energy of the system. D. enthalpy of the universe. E. entropy of the universe.
E
Where do the catabolic products of fatty acid breakdown enter into the citric acid cycle? A. pyruvate B. succinyl CoA C. α-ketoglutarate D. malate or fumarate E. acetyl CoA
E
Where does glycolysis take place in eukaryotic cells? A. mitochondrial inner membrane B. mitochondrial outer membrane C. mitochondrial matrix D. mitochondrial intermembrane space E. cytosol
E
Which kind of metabolic poison would most directly interfere with glycolysis? A. an agent that reacts with NADH and oxidizes it to NAD+ B. an agent that reacts with oxygen and depletes its concentration in the cell C. an agent that binds to pyruvate and inactivates it D. an agent that blocks the passage of electrons along the electron transport chain E. an agent that closely mimics the structure of glucose but is not metabolized
E
Which of the following is most similar in structure to ATP? A. an amino acid with three phosphate groups attached B. a phospholipid C. a pentose sugar D. a DNA nucleotide E. an RNA nucleotide
E
Which of the following is true of metabolism in its entirety in all organisms? A. Metabolism uses all of an organism's resources. B. Metabolism depends on a constant supply of energy from food. C. Metabolism manages the increase of entropy in an organism. D. Metabolism depends on an organism's adequate hydration. E. Metabolism consists of all the energy transformation reactions in an organism.
E
Which of the following represents the activation energy needed for the noncatalyzed reverse reaction, C + D → A + B, in the figure? A. a B. b C. c D. d E. e
E
Why are carbohydrates and fats considered high energy foods? A. They can have very long carbon skeletons. B. They have a lot of oxygen atoms. C. They are easily reduced. D. They have no nitrogen in their makeup. E. They have a lot of electrons associated with hydrogen.
E
Why does the oxidation of organic compounds by molecular oxygen to produce CO2 and water release free energy? A. The electrons have a higher potential energy when associated with water and CO2 than they do in organic compounds. B. The oxidation of organic compounds can be used to make ATP. C. The covalent bonds in organic molecules and molecular oxygen have more kinetic energy than the covalent bonds in water and carbon dioxide. D. The covalent bond in O2 is unstable and easily broken by electrons from organic molecules. E. Electrons are being moved from atoms that have a lower affinity for electrons (such as C) to atoms with a higher affinity for electrons (such as O).
E
Why is glycolysis considered to be one of the first metabolic pathways to have evolved? A. It relies on chemiosmosis, which is a metabolic mechanism present only in the first cells' prokaryotic cells. B. It is found in prokaryotic cells but not in eukaryotic cells. C. It requires the presence of membrane-enclosed cell organelles found only in eukaryotic cells. D. It produces much less ATP than does oxidative phosphorylation. E. It does not involve organelles or specialized structures, does not require oxygen, and is present in most organisms.
E
Yeast cells that have defective mitochondria incapable of respiration will be able to grow by catabolizing which of the following carbon sources for energy? A. proteins B. Such yeast cells will not be capable of catabolizing any food molecules, and will therefore die. C. glucose, proteins, and fatty acids D. fatty acids E. glucose
E
You have a friend who lost 7 kg (about 15 pounds) of fat on a regimen of strict diet and exercise. How did the fat leave her body? A. It was converted to ATP, which weighs much less than fat. B. It was broken down to amino acids and eliminated from the body. C. It was converted to urine and eliminated from the body. D. It was converted to heat and then released. E. It was released as CO2 and H2O.
E
